The comedian – who stepped down as co-host of the baking show last year – said he and his Little Britain co-star Walliams thought it was time to work together again.
He said on The Zoe Ball Breakfast Show BBC Radio 2: “Me and David Walliams have started writing together again.
“We just thought it was time, so we quit our jobs and decided to do that.”
“We've got an idea for a new show and we need a few more brainstorming sessions but we know what we want the show to be, what the concept of it is,” he said.
"We're really excited about it. It will be a show with us playing lots of characters.
"But we have to write the treatment for it and we have to go and pitch it and see if anyone wants to make it."
He said if someone wants to make the show "we'll be thrilled to do it".
Lucas, 48, stepped down from Bake Off in December after co-hosting for three series alongside Noel Fielding.
He said it had been a “delicious” experience but that he was “cheerfully passing the baguette” onto someone else.
Walliams, 51, was at the centre of a controversy last year when the Guardian reported that he had been overheard making insulting comments about some of those auditioning while on the BGT set.
He apologised for his “disrespectful comments”, saying they were part of private conversations that were never meant to be shared but that he was sorry.
Watch: Matt Lucas promises 'I didn’t really have world domination on my mind!'