I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

 That's something to discuss with the DM and the other players - you don't want to make a PC which the others dislike and which you feel uncomfortable playing in character, so perhaps reserve this character for a more chaotic game in the future and try to make something more in line with what the DM has planned and what the other player's characters are like. There's no point playing an evil assassin plotting to overthrow the overworld if the rest of the party like the overworld as it is and are fighting to save it, and the DMs premise for the campaign is that the world is being pitched into chaos and the party needs to save it.

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

 I actually think this could be okay, if you think about that in secret, as in kiling the leaders as soon as you finish interacting with them, also sparing the DM.

It could be okay, but it could also get pretty bad. First of all I'd make sure that the character itself is not some edgy loner who's constantly scheming against the party itself... You don't want a hostile party dynamic unless everyone involved is prepared for that kind of stuff.

Secondly, having some overall evil scheme is alright imo, but it'd probably be best if it's something that doesn't negatively impact the rest of the party. Perhaps your character's mission is the target a specific set of NPC's whose death would no sabotage the entire campaign.

Adding on to the advice above, make sure that you discuss all of this with your DM. The DM is your co-conspirator, not your enemy. By working together you can make sure that you don't accidentally destroy the DM's plot, and the DM might also give you some opportunities to work towards your goal.

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

 At the end of the day, it's all about what works for your table and group. That being said,

Always, always, consider how selfish your character is given that it's a cooperative game..

Adding on to what everyone else has said, don't do it without the DM's permission. Depending on the campaign, it could be really amazing, or fail within 2 sessions. So make sure to ask the DM about it. If you want the party's characters to know, tell them in roleplay AND out of roleplay. If not, you should probably do it at a session zero or if you aren't doing one, maybe a day or two before the first session. Either way, you should just make sure that everyone is ok with it. There have been a few times in my time playing D&D where the players or even the DM have done something that none of us were prepared for or ok with. So talk to them about it before the campaign!!!!!!!!

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

 This sounds really extreme. There are a lot of ways to explore the same concepts without being so disruptive.

What does "overthrow the world" mean? "Murder all the kings" is not really a realistic end goal, it's a means to achieve something. When the current establishment is gone, what do they want in its place? Do they just want total anarchy or something else? There are lots of ways to destabilize the current order that fall short of killing kings (which should be out of the reach of a low level assassin anyway), and if there is an alternative you want in place there are plenty of ways to advocate for that. What I'm getting at is that you develop some actual beliefs about how the world should work and you can apply them to all kinds of smaller stakes situations.

The other variable here is how much you act on what you want. You can totally want to murder the king that just gave you a quest, but you can choose not to because of your loyalty to the party or because you want the quest reward or because it gets you into his inner circle so you can destabilize it or a dozen other reasons. Having those desires and motivations come in to conflict makes for a lot of drama and a really interesting character develops from it. 

First of all, you should cooperate with other PCs, and not play some kill-everybody murder hobo, if this char is good with following along with the story, great, but there’s a good chance this character could destroy the campaign, second, did you discuss this character with your DM?, whether or not you discussed  your character and their intentions can make or break your game.

It’s really good that you recognize this character concept might be problematic. Most people just go ahead with it and cause problems. They find out the hard way that edgy, anti-social loners don’t work in D&D, because the rest of the players (not characters) get mad at them, because as others have said, you are part of a party. Side note: is your DM ok with you making an evil character, because your concept is unquestionably evil.
While I agree with the others that you need to check with your DM, really you need to check with the whole table. See how far you can push it before your fun starts bumping up against their fun. 
Moreover, this isn’t a character concept as much as it’s an idea for an entire campaign — either doing it, or stopping others from doing it. Again, it doesn’t work as part of a team to say that while the adventure is happening here, you really need to go three kingdoms over and do a thing. At that point the most logical solution would be for the character to leave the party, which is often what ends up happening in these kinds of situations. In the end, my guess is, you need a new character concept. 

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord. I feel if I play this then it might end out badly for me and my party and might ruin the game. 

It depends, as long as you aren't taking too much of the fun out of it, then you'll be fine, Personally id talk with the rest of the group seeing if they think it'll ruin the fun, but I think you'll be fine

My usual rule of thumb is "do what you want, just don't complain about the consequences". If your character dies 45 mins into the first session because of some fool stunt, so be it. If it's the rest of the party killing your character, so be it. Two caveats: 1) you don't get to hide something like this from the other players and 2) I can occasionally set some time aside for a short solo session, but don't expect it to be a regular thing - my time goes to everyone equally, I'm not devoting lots of it to players who keep going off doing their own thing alone.

Quote from Bobbill111 >>

I'm at the moment playing a character who's a drow assassin who wants to help over throw the over world by killing royals and spreading discord.

Help who? Is this a thing in the setting? 

As many others have said, talk to your DM. If it doesn’t work for the campaign then save that character for later. But maybe the DM might incorporate this into the campaign. Starting small, a quest could be given to the party that seems like a normal quest yet has ramifications 15+ sessions down the line leading to your character assassinating a king.

Maybe the party is being deceived into helping overthrow a kingdom thinking they are doing good.

Maybe your character becomes the BBEG’s co-conspirator.

Or maybe the king is just bad and needs to be removed but you don’t know it yet until much further in the campaign. 

It’s up to your DM if this will work or not. 

Just remember, you are not the only player at the table   And other players have as much right to having fun as you do.

Im with a rogue cult who think if they can destabilize the over world and then the drow can take there rightful place on the surface.

do you think it might work if I only kill them after we've done everything we need to do with them. Or if you think there's no way any of this would work it'd might be helpful for some ideas for a different character kind of like this.

This is really up to the DM, it seems like you're trying to "pre game".  Your Drow sounds like they're basically part of a terrorist group trying to upset the surface world so that the Drow can take over.  What does the rest of the party do?  Is the DM going to provide space for a global or at least continental campaign of assassination on top of what the rest of the party does.  "Overthrowing the world" is a bit much for a side quest.  If I understand the game right and this agenda is not in fact what's driving the campaign, I think your affiliation with a terror group could probably best and realistically be handled by being given side assignments to aid and abet the terror group's plans.  But again, you can pregame as much as you want on the board, but it doesn't mean anything unless the actually game you're in is on board and you do that by centering the conversation there.  Here is good for brainstorming, but that's it.

If you ever watch The Expanse, there's some good guidance on how characters affiliated with radical agendas can mix in with a more middle of the road aligned group.  There's tension, but it can be done.  

Your character would have no way to know if you've done everything you need to do with an NPC. Even then, the actions you are describing seem pretty evil, and could be a problem for lots of people.

The easiest thing I can think of for something similar is that your character belonged to this cult, but then they went to the surface, made some friends with people of other races, and also saw that (at least some of) the kings and queens and rulers on the surface are actually good people. You realized there may be another way. Then you had a change of heart and decided that the cult is too extreme. Working with your DM, you could then have an angry cult chasing after you for leaving them. Or you could find it hard to completely give up your old ways, and decide that maybe you don't want to kill all of the rulers in the world, just the bad ones. Other players might get behind that idea. So you can maybe carve out a small place for the drow to come to the surface, and then they'd all instantly regret it since they have sunlight sensitivity.

Quote from Xalthu The easiest thing I can think of for something similar is that your character belonged to this cult, but then they went to the surface, made some friends with people of other races, and also saw that (at least some of) the kings and queens and rulers on the surface are actually good people. You realized there may be another way. Then you had a change of heart and decided that the cult is too extreme. Working with your DM, you could then have an angry cult chasing after you for leaving them. Or you could find it hard to completely give up your old ways, and decide that maybe you don't want to kill all of the rulers in the world, just the bad ones. Other players might get behind that idea. So you can maybe carve out a small place for the drow to come to the surface, and then they'd all instantly regret it since they have sunlight sensitivity.

 Ok I have something along these lines. I killed one king and kidnapped his son (another player). The cult leader uses dark magic on him and I, seeing this, kill the cult leader and flee with the prince.

Again, make sure the DM is ok with your plans, but it sounds reasonable. Also, check in with the player who’s character is the prince. They’ll probably want a say in what their character is doing, and it probably won’t be sitting there passively while you rescue them. 

yep. thanks for the advice