O'Brien will replace former lead assistant Terry Stotts on the Mavs' bench after Stotts took the head coaching position with the Portland Trail Blazers. Dallas was also interested in Jay Triano and Steve Clifford before they accepted offers elsewhere, according to ESPN.
In his last head coaching gig, it was O'Brien who replaced Carlisle after he was fired from the Indiana Pacers following the 2006-07 season. O'Brien was fired by Larry Bird in the middle of the 2010-11 season after a poor 17-27 start. He has also coached the Boston Celtics and Philadelphia 76ers.
The 60-year-old brings 630 games of head coaching experience to the Mavericks. O'Brien went 303-327 in those games.
For the Mavericks, this continues a long line of coaching turnover. Carlisle's former lead assistant, Dwane Casey, left in 2011 for the Toronto Raptors' head position before Stotts left for Portland this year.