I am currently playing a Goblin Warlock 6 (Celestial)/Rogue (Mastermind): 4, with the Pact of the Tome, Book of ancient secrets, One with Shadows, and Mask of many faces as the invocations, and has the Arcanist and Diplomat feats. Basically they are a swiss army knife healer. Can basically heal at distance, sneak, talk, and do just about anything. Not a combat monster by any means, or a powerful mage (the other three players are taking those spots), so a character that can pretty much do EVERYTHING else is useful. 

I'm playing a Hexblade/Arcane Trickster in my current campaign. The invocations i find to be the most helpful at the moment are devils sight and misty visions. Depending how you play your rogue, the invocations that help with stealth and deception will be the most helpful.

Running a 7th level Hexblade, Pact of the Blade warlock + 3rd level Rogue Swashbuckler build. I have 7 levels of warlock; I was going to stop at 5 but wanted extra invocations and 4th level spells. This turned out to be to my benefit as at 4th level I was able to take the Shadow of Moil spell which allows me to gain sneak attack on essentially any enemy who attempts to attack me or have advantage to hide (which I can do as a bonus action as a rogue) allowing me to have sneak attack on an attack in a round. More or less I have sneak attack on most attacks in a battle.

I also like using the Shadow Blade spell which grants me advantage when I'm in dim lighting conditions (Our campaign is set in the Underdark so I ALWAYS have advantage).

Plus with the Thirsting Blade invocation, I gain an extra attack, so if I miss my first attack I don't lose my chance to do sneak attack once per round. All in all, I'm dealing insane damage every round, usually at least 25 damage per attack with more if I get sneak attack.

I'm planning on continuing to take rouge levels to maximize my sneak attack damage going forward.

Hexblade/Swashbuckler is a great build for pure melee damage output, and with the Improved Pact Weapon invocation, potentially even a ranged build.

Quote from rome1717 >>

Looking for ideas with this multi class. Specifically how many levels of each did you take? Did you go back and forth or ditch one class after you got what you needed from the other? 

Going back and forth just delays returns. I have not done this and I do not recommend it. 

For a melee-heave character, I recommend Rogue until you get a class feature you want, like Cunning Action (L2), your Archetype (L3), ASI (L4), Uncanny Dodge (L5), Expertise (L6), etc.

Then Warlock for the features you want - level 5 is a good breaking point, as it gives two level 3 spells per short rest and three invocations.

Then advance in the class you want more of. Consider Booming Blade or Green Flame Blade as a melee heavy rogue.

In fact, my Warlock hit level 5 and has just taken one level of Sorcerer (doubling my spells, etc.), and will now advance to (probably) level 9 Warlock before considering more Sorcerer levels.

In my DiA game, I’m playing a dispater tiefling roguelock. Mainly took it for being charisma SAD to take advantage of tiefling racial boost and to be an even better party face/social character without losing combat effectiveness. Only taking 2 levels of warlock costs the rogue 1d6 of sneak attack progression, but SAD Cha and hex more than makes up for a 1d6 loss. Plus, the tiefling racial spell abilities are amazingly useful. Dispater/Glasya are the ones to pick.

point buy stats were 8/13*/14/12/12/14**, with dispater tiefling pushing dex to 14 and charisma to 16

I started as Rogue 1 for the proficiencies and expertise. I then immediately went into Warlock for 2 levels, picking hexblade for medium armor/shield (breastplate with 14 dex and shield = 18 AC @ lv2), charisma SAD and for increased crit range on hexblades curse target. Picked up Hex and Shield for spells, with Booming Blade and Eldritch Blast for Cantrips. 2nd warlock level for agonizing blast for a ranged option (no sneak attack, but I’m focusing melee) and eldritch sight for detect magic at will. Rest of levels went straight to rogue, picking arcane trickster mainly for spell slots to be used with Shield/Absorb Elements, and obviously all the utility that comes with being an arcane caster. Avoid any damaging spells because your int is low, just use slots for defense/utility.

ASI’s go to charisma to 20, but feel free to delay ASI to get the Sentinel feat, or even the Mage Slayer feat if your campaign is heavy on magic enemies. Both feats give you more opportunities for sneak attacks. Also, dropping the shield for an offhand weapon will give more chances at sneak attacks but will have reduced effect (only 1 weapon can be hexblade cha based) and you lose your bonus action flexibility. I recommend cha 18, sentinel, cha 20 in that order. 

So I have been thinking (there are a lot of problems with this idea. It's just the framework) I wanna go at least rogue 5 for the resistance and then wanted to combine it with bladeward for 100% physical resistance (which is really broken and I could see why that's just not allowed) But the though is warlock gets all of it's abilities at 14 right ,they upgrade from there but nothing new, and rogue only needs 5. so either a 14 6 split or a 15 5. (then I realized you could just take magic initiate and go full rogue but damn it I want my roguelock) any advice on that kind of a build? (can you tell I am *very* new?)

I’m just starting out with a Rogue/Warlock/Fighter build that is focused on Ranged attacks for a Descent into Avernus campaign. Level 3 Rogue Assassin gets Assassinate, which makes a surprise round attack automatically a critical, doubling all damage dice rolled (PHB includes sneak attack dice). Eldritch Smite invocation lets you sack a spell slot for 1d8 plus 1d8 per spell level force damage on the attack, and as Warlock spells lots automatically level to the highest with your class level, this is a minimum of 4d8 extra force damage. Improved Pact Weapon for a +1 Heavy Crossbow means a surprise attack at level 8 will deal 2d10+4d6+8d8+DEX+1 damage, and this can be snuck into places weapons aren’t normally allowed, like a Throne room. Dismiss the weapon after and there’s no proof it was ever you.

I am currently playing as a dark elf who had found a way to extend his life indefinitely. he's patorn is a great old one. and the way i have been playing him my party is telling me i should multi class to rouge. so i was thinking going arcane trickster.  and the way my Dark elf extended his life is by putting his soul into an item. the way my DM and I flavored it, him is that his very knowlegable in Magical items, and i also can take control over a humanoid if they fail my spell save dc, and i can chose not to take over the body.  What would you suggest the levels between rouge and warlock . 

Since Warlock require 13 charisma to multiclass the most natural Rogue class is the Swashbuckler, which is also one of my favourite Rogue classes (along with Arcane Trickster).

I will use a High Elf as the basis (since getting an extra cantrip is always good) and since mending isn't in the Warlock spell list I'll take that.

Stats I'll use the Tasha's/Adventurer League rules to move the High Elf's +1 Intelligence to Charisma so we can start with 16 charisma. Stats 8/16/14/10/10/16.

Background: My favourite for Rogue is Charlatan, which gives proficiency in deception, sleight of hand, disguise kit, and forgery kit. Sailor/Pirate is another possible option.

First level Rogue. You lose a skill proficiency if you go from Warlock to Rogue, and Rogue starts with better equipment.

You're getting perception from Elf, deception and sleight of hand from Charlatan, pick four more. I'd go with athletics, acrobatics, stealth, and persuasion. I'd put expertise on persuasion and perception. You will be extremely persuasive.

At level 2 I'd take the first level in Warlock. I think the Celestial warlock is the better option over Hexblade for a Rogue build. You get light and sacred flame as cantrips, and can take two Warlock cantrips, I'd take eldritch blast and prestidigitation. Prestidigitation pairs well with mending to allow you to stay nice and neat, which is important for a Swashbuckler.

Level 3 and 4 I'd continue as Warlock, and take the Pact of the Tome. Three levels of Warlock give you 2nd level spell slots, the Book of Ancient Secrets gives you access to all ritual spells up to level 2, which is most of them, and Agonizing Blast maximizes damage from your Eldritch Blast.

I would then switch back to Rogue and continue the game as a Rogue with some Warlock abilities.

Lets Begin this by Saying I'm Bat man.

Tiefling Features:

• Within 60 feet of you, treat dim light as bright, darkness as dim light
• Gain fire resistance
• Can cast the minor illusion cantrip. At 3rd level, disguise self (1/day). At 5th level, invisibility (1/day) (use Cha for DCs)

Sailor Feature:

• You can arrange free passage on a ship for your party (in this case everyones boat is your batboat)

Rogue Features:

• Sneak Attack (will be 6d6)
• Understand a secret language
• Double proficiency with chosen skills (Sleight of Hand,Stealth)
• You can dash, disengage, or hide as a bonus action
• Rogue Archetype: Swashbuckler
• Creatures you attack can't make attacks of opportunity against you that turn
• Gain Cha mod to initiative
• You can sneak attack a creature if it's the only one adjacent to you
• Crossbow Expert: You don't have disadvantage from adjacent enemies on ranged attacks, you can load crossbows faster, and you can make a bonus action attack with a hand crossbow after attacking with a one-handed weapon
• You can use a reaction to take half damage when hit by a foe that you see
• Double proficiency with chosen skills (intimidation, Thieve tools)

Warlock Features:

• Warlock Archetype: Hexblade
• The spells shield and wrathful smite are added to the warlock spell list for you
• 1/rest as a bonus action you can curse a creature for 1 minute, healing level + Cha mod hp when it dies, critting it on a 19, and dealing it proficiency bonus extra damage
• Gain martial weapon, shield, and medium armor proficiency
• You can use Charisma for attack and damage rolls with your pact weapons and one one-handed weapon you choose at the start of each day
• Disguise Self Expert: You don't use a spell slot when casting disguise self

Rogue Features:

• When you would make a Dex save for half damage, you take no damage if you pass or half damage if you do not
• You can charm a creature with a persuasion check (see rules)
• Medium Armor Master: Your max Dex to AC in medium armor increases to 3, and medium armor no longer causes disadvantage on stealth
• When you make a proficient check, you can take 10 after the roll
• Sharpshooter: Your ranged attacks ignore � and � cover, don't have disadvantage from long range, and you can take -5 to a ranged attack for +10 damage

Warlock Features:

• Blade: You gain the ability to conjure a magical weapon (see rules)
• Improved Pact Weapon: You can conjure bows and crossbows, your conjured weapons are +1, and you can use them as a focus
• The spells blur and branding smite are added to the warlock spell list for you
• Extra Attack: You can make two attacks with your pact weapon as an action
• The spells blink and elemental weapon are added to the warlock spell list for you
• 1/day you can raise a specter from the corpse of a humanoid you killed (see rules)
• Silent Image Expert: You don't use a spell slot when casting silent image
• The spells phantasmal killer and staggering smite are added to the warlock spell list for you
• Resilient: You gain proficiency with one save and +1 to that ability

You end this build with 143 HP an AC of 20 STR 8 DEX 16 CON 14 INT 12 WIS 10 CHA 20. You'll get 6d6 sneak attack, You'll be going first with a nice +8 initiative, get to curse offering more crits, 2 fourth level spells on every short rest, Cross bow master but think of booming blade with sneak attack and no AOP when you bonus action dash away. You can innately cast invisibility once a day! Imagine if you will the shadow such a character would cast? 

I know this is a really post but I'm needing some help with my build and I'm hoping that this does the trick.

I'm playing a level one rouge and then level two I want to multi-class into the fathomless Warlock and then continue leveling the rouge until I can become the swashbuckler rouge at level three and then from there I was planning on dumping the rest into warlock any advice?

I think warlock 5 is the max if you want to be martial, I don’t like ALWAYS doing hexblade cus it’s repetitive and unoriginal so I’d probably go undead for temp up and the fact you can frighten people once a round then I’d go phantom rogue for both theme and synergy, your a skill monkey that has decent battlefield control, not OP at all but useable and more importantly fun

I decide to go 3 lvls of rouge Swashbuckler first and then fathomless warlock, i get what ur saying about hex , im also doing Armor of Agytha to raise temp hp with bonus cold damage. Any other suggestions though?

With the new character creation rules it'll be easier to slide between classes.

For example you can key the racial spells races get to charisma, so you can then shift easily into warlock.

A High Elf with the Magic Initiate feat will have three cantrips and a level 1 spell that will be a good addition to the Warlock list.

Choosing Divine or Primal would allow you to take cure wounds or healing word as a spell, and that might come in useful even on an arcane class.

Our group is playing through Decent Into Avernus...im playing as an arcane trickster rogue...however we have run into a serious problem...after a fight with some undead we are all infected with a virus that will turn us into a zombie in 24 hours unless we find help.  the problem is, that we're literally in a dungeon, in elturel (which is currently in avernus).  we've had a few weeks between sessions and i had an idea...my character is going to make a pact with a fiend to remove the virus in exchange for his soul...  so after this evening's session i will be Arcane Trickster Rogue/Fiend pact Warlock.  Im hoping its a good combo...will be my first multi-class and i love that the decisions are being forced by the story instead of me just getting to choose what i want.

Quote from mutenoise84 >>

Our group is playing through Decent Into Avernus...im playing as an arcane trickster rogue...however we have run into a serious problem...after a fight with some undead we are all infected with a virus that will turn us into a zombie in 24 hours unless we find help.  the problem is, that we're literally in a dungeon, in elturel (which is currently in avernus).  we've had a few weeks between sessions and i had an idea...my character is going to make a pact with a fiend to remove the virus in exchange for his soul...  so after this evening's session i will be Arcane Trickster Rogue/Fiend pact Warlock.  Im hoping its a good combo...will be my first multi-class and i love that the decisions are being forced by the story instead of me just getting to choose what i want.

 I think thats great, personally, my DM lets us multiclass w/out level limits, so it doesn't have to add up to 20, it can go beyond, and he says it will be a long campaign, so I'm planning to put 15 levels into Arcane Trickster, then on and off Gloomstalker, then when I hit Lv 15 on Gloomstalker, I will multiclass into efreeti Warlock.

Been thinking about this as well. Based on the replies, the opinions on it are mixed.