The comedy and musical Amnesty fundraiser, which will air on Channel 4, takes place at New York City's Radio City Music Hall on Sunday, March 4.
Coldplay, Jon Stewart, Stephen Colbert, Mumford & Sons, Russell Brand and Reggie Watts were previously revealed as part of the lineup.
Fred Armisen, Hannibal Buress, David Cross, Noel Fielding and Rashida Jones will also appear at the event.
Other new names for the bill include Seth Meyers, Bob Odenkirk, Andy Samberg, Peter Serafinowicz and Sarah Silverman.
Channel 4, who will be showing the event just days after it takes place in the US, commented: "We're very proud to be working with Amnesty International and to be able to bring the show to UK audiences. It's a brilliant lineup in an iconic venue.
"Even with over 20 top names already announced, more comedy and music stars will be announced over the coming weeks, as well as the winner of 'The World's Shortest Gig' - a competition for an aspiring UK comedian to win a 15-second slot on stage at The Secret Policeman's Ball."
Amnesty International's Kerry Moscogiuri said: "We're extremely excited by the great host of talent who have given up their time to take part in Amnesty's Secret Policeman's Ball. We expect this will be a great evening of entertainment that will also succeed in throwing a spotlight on the importance of Amnesty's work on defending all human rights, and in particular free speech.
"Campaigning for freedom of expression remains a fundamental part of Amnesty's campaigning work. Last week the organisation called for the release of social media activist Park Jeonggeun from South Korea after he retweeted messages from North Korea's official government Twitter account."
> Coldplay, Russell Brand for Secret Policeman's Ball in New York