The news broke Tuesday from various media outlets, including ESPN.com and CBS Sports.
With Martin sliding into the No. 00's driver's seat at MWR, the driver who currently occupies that seat—David Reutimann—appears to be without a job.
ESPN.com confirmed Tuesday that when asked about the situation, Reutimann told reporters, "Talk to Michael," referring to his team owner, Waltrip.
Reutimann joined MWR in 2007 and was a valuable asset to Waltrip's upstart team through 2010, winning two races, earning 23 top-10 finishes and eleven top-fives.
But this season, the Zephyrhills, Fla. native has struggled, posting just two top-10 finishes and one top-five, with one qualifying pole and zero wins to his credit.
Martin moves to MWR from Hendrick Motorsports after a three-year stint that featured five wins, 32 top-10s and 21 top-fives in 2009-2010.
This season, the 52-year-old Batesville, Arkansas native has yet to reach victory lane and has just 10 top-10s and two top-five finishes.
MWR's addition of Martin will complete a "silly season" revamp that added Clint Bowyer just over three weeks ago after stealing the driver away from Richard Childress Racing.
The new and improved MWR stable will consist of veteran team driver Martin Truex, Jr. in the NAPA-sponsored No. 56, Bowyer in the No. 15 Five-Hour Energy car, and Martin in the No. 00, which will keep Aaron's on the car for the announced limited schedule.
Waltrip will compete in most or all of the four restrictor plate races on the schedule, likely in the No. 00.
Current Red Bull driver Kasey Kahne, who is driving for the team this season in a sort of holdover season in between full-time contracts at Richard Petty Motorsports and Hendrick, will replace Martin in the No. 5 car next season.
MWR will make an announcement Friday at Texas Motor Speedway unveiling its official 2012 plans.