Mitchell will replace Rob Schrab who left the second 'Lego Movie' due to creative differences, according to The Hollywood Reporter.
The sequel to 2014 hit adventure fantasy is scheduled for February 8, 2019 Stateside.
It is unclear if any of the original voice cast that include Chris Pratt, Will Ferrell, Elizabeth Banks, Will Arnett, Liam Neeson and Morgan Freeman will return to the follow-up story.