Atkinson is replacing Armindo Araujo who has been rested by the team to "regain his focus". The Australian will contest the remaining five rounds with Team Portugal in a car he has not yet driven.
"MINI has provided me with an awesome opportunity to return to the world championship and I'm stoked to be back as a lead driver for a great manufacturer and for the remainder of the 2012 season," Atkinson said.
The 32 year-old former Subaru WRC works driver - and former Asia Pacific Super 1600 championship winner - first drove at the top-level in 2004 at Rally New Zealand.
In 2006 he secured a full-time drive with Subaru and had a wild year, finishing tenth in the championship.
During 2007 he was a vastly improved driver, scoring podiums and stage wins.
At the end of the 2008 season, Subaru withdrew from the sport, marooning both Atkinson and team leader Petter Solberg.
Atkinson's first rally will be on the tarmac stages of the Rallye Deutschland starting August 24, back with co-driver Belgian Stephane Prevot.
"It'll be his first time in a MINI on the test this weekend, but we're confident that Chris can handle any car he lays his hands on and his MINI will love him within minutes," team manager Bruno di Pianto said.
"We're all very much looking forward to working with him and Stéphane and seeing what surprises Rallye Deutschland has to offer!"