Walliams, 50, posted on social media images of himself and Lucas, 48, in costume as the Bad Romance and Sunflower singers.
The Come Fly With Me stars will also take on the guise of Michael Ball and Alfie Boe in the name of comedy.
The singers teamed up to release a Christmas album Together At Christmas last year.
Walliams and Lucas were previously unveiled as Miley Cyrus and her dad, Billy-Ray Cyrus in a promotion for their Red Nose Day Rock Profiles.
The comedians were a double act for years enjoying huge success with their sketch shows Little Britain and Come Fly With Me, but clashed during the Little Britain live tour in the Noughties and have barely worked together since 2011.
Walliams and Lucas briefly reunited for Radio 4 sketch Little Brexit in 2019 and have since said that they're in contact much more regularly.
Rock Profiles dates back to 1999 and will get a fresh sketch as part of next week's Comic Relief schedule at the BBC, where Vernon Kay will meet some famous faces at the studio ahead of the launch of the Comic Relief single.
Lucas said: "It’s been really fun giving the Rock Profile treatment to a host of stars who weren’t even twinkles in our eyes when we first did the show nearly 25 years ago."
Walliams added: "It has been a blast working with Matt on Rock Profile again. I can’t wait for everyone to see our brand new characters."
Kay, who stars with them, said: "I have been watching David and Matt’s sketches for as long as I can remember, so I am super excited to get to be part of one myself. Thankfully I will be playing myself in Rock Profile, so I’ll be saving David or Matt the embarrassment of attempting my accent!"
Walliams and Lucas aren't the only double act getting back together for Comic Relief - Dawn French and Jennifer Saunders are set to reprise their characters The Extras in a sketch show version of The Repair Shop, and Strictly Come Dancing winners Rose Ayling-Ellis and Giovanni Pernice will dance a waltz.
Other highlights include Kylie Minogue joining the residents of Button House in a Ghosts special, Stephen Fry and Sue Perkins reading the CBeebies Bedtime Stories, and Jack Whitehall taking on footballers Mason Mount and Declan Rice in the Mini Golf Challenge.
A special episode of Glow Up sees Lady Leshurr, Nikki Lilly, Roman Kemp, Snoochie Shy and The Vivienne compete as make-up artists, while Chris Eubank, Harry Hill, Claudia Winkleman and Nina Wadia have a turn at lie detecting contest This Is MY House.
Taking on the challenges this year are Tom Daley, who will make a 290-mile journey from the Aquatics Centre in London, where he won his first Olympic medal, to his hometown of Plymouth by rowing, marathon running, open water swimming and cycling; and Jordan North, who will row from London to Burnley over five days.
Comic Relief's main night of programming airs on Friday, 18 March from 7pm on BBC One.
Watch: Tom Daley discuss his gruelling Comic Relief trek