Lawson has been Red Bull reserve since 2022 and filled in for Ricciardo at five races last year when the eight-time Grand Prix winner was injured.
"Daniel has been a true gentleman both on and off the track and never without that smile. He will be missed, but will always hold a special place within the Red Bull family," said team boss Laurent Mekies in a statement.
"I’d also like to take this opportunity to welcome Liam. He already knows the team well. He drove for us last season, and coped well under difficult circumstances, so it’ll be a natural transition."
Italy-based RB had initially posted a 'thank you' message on social media.
"I’ve loved this sport my whole life. It’s wild and wonderful and been a journey," Ricciardo said separately on social media.
"To the teams and individuals that have played their part, thank you. To the fans who love the sport sometimes more than me haha thank you. It’ll always have its highs and lows but it’s been fun and truth be told I wouldn’t change it.
"Until the next adventure."
