Mostert will share a BMW Team RLL M8 GTE with John Edwards, Jesse Krohn, and Augusto Farfus in the IMSA SportsCar Championship season opener.
Driving the team's second car will be the 2019 event class winners Connor De Phillippi, Bruno Spengler, Colton Herta, and Philipp Eng.
“Once again BMW has given us a really good core of drivers to compete with in 2020,” said team boss Bobby Rahal.
“I'm pleased with the continuity we have with John Edwards, Connor De Phillippi and Jesse Krohn returning.
“It is always a good thing to be able to build on the foundation you have created when possible.
“Bruno Spengler is a really good team player and will be a great addition. I have a lot of respect for him and everything he has done in the DTM.
“We are happy that Augusto Farfus, Colton Herta and Philipp Eng, who helped us win the 2019 Rolex 24 at Daytona, will be returning to the line-up for that race and are also looking forward to welcoming Chaz Mostert back.
“We thank Tom Blomqvist for his commitment to the team this season and wish him luck in his endeavours.”
Mostert competed in last year's 24 Hours of Daytona with Rahal Letterman Lanigan Racing, and raced at Petit Le Mans in 2018 with the squad.
“I am looking forward to the 2020 IMSA season and am confident that, with our four regular drivers, we have everything in place to make it a successful year,” said Jens Marquardt, BMW Group Motorsport Director.
“We are entering our twelfth year together with BMW Team RLL. We are also largely going with continuity when it comes to the drivers.
“John Edwards and Connor De Phillippi have a lot of experience of the IMSA series, and Jesse Krohn also did a good job in his second IMSA season in 2019.
“All three know the BMW M8 GTE, the series and the circuits in North America very well. Bruno Spengler has not only shown his class throughout his long DTM career, but also in his many GT outings on the endurance scene. I am sure that he will be a real asset to BMW Team RLL.
“At this point, I would particularly like to thank Tom Blomqvist for the great collaboration over the past five years. Whether in the DTM, WEC, Formula E or the IMSA series, like last season, Tom has coped well on any terrain. We wish him all the best for the future.
“The IMSA season traditionally starts with the ultimate highlight – the 24 Hours of Daytona. It will be nice to see last year's four GTLM winners – Augusto, Connor, Colton and Philipp – back at the wheel of the BMW M8 GTE there.”
The Rolex 24 at Daytona is set to take place on January 25-26 with the Roar Before the 24, a pre-Daytona test, on January 3-5.