A good lawyer always tells the truth professionally. At least in common law countries like mine. I’m going to generally speak USian, but our northerly neighbors are likely similar as are the brits, kiwis, and aussies. I’m not certain a prosecutor in my country could do well without lying at all, but that’s an entirely different problem of cultural collapse.

A defense lawyer defends both innocent and guilty as their zealous advocate. Their job is to poke doubt in the prosecution’s narrative and possibly provide a counter narrative, but generally challenge everything the prosecution can’t prove beyond a reasonable doubt. They may also just be pleading for lesser sentencing. That’s part of how plea deals became so common here. They also don’t say the client is innocent, they state that the client is pleading guilty or not guilty. People can be not guilty and have done it as well, so long as they either have a lawful reason to do the action, or are incapable of legal guilt such as by insanity. They also have a lot of things they aren’t allowed to speak on and are supposed to just say that instead of lying. Copaganda has attempted to convince the masses that these people are lying scumbags who get bad guys on the streets instead of defenders of liberty who force the government to actually prove people did what they claim they did.

A prosecutor’s job is to take the evidence and build and reinforce a narrative that can withhold the defense’s scrutiny. It should be wholly truthful to the best of their knowledge. The goal is to convince the jury beyond a reasonable doubt that the accused is guilty and then advocate for a sentence they feel is fair.

Then you’ve got all sorts of other lawyers. Cause lawyers like human rights and environmental lawyers largely argue over interpretations of laws and whether actions violate them. These people ought to believe what they say. Business and corporate lawyers don’t even have room to lie, they’re just building contracts and such.