Josh McDaniels agreed to terms on a multiyear contract to rejoin the New England Patriots' coaching staff, a league source said Saturday.
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McDaniels, who could join the Patriots' staff as soon as Monday, will serve as an assistant until the season ends, when he will become the offensive coordinator. Bill O'Brien, New England's current offensive coordinator, accepted the head-coaching job at Penn State this week but will stay with the Patriots throughout the playoffs.
The Patriots have a Jan. 14 home game against the winner of Sunday night's Pittsburgh Steelers-Denver Broncoswild-card game.
"It'll be full-go with the Patriots," O'Brien said Sunday at the Penn State-Indiana men's basketball game, according to the Boston Herald. "That's a question you'll have to ask Bill (Belichick) as far as Josh coming in. I'm not privy to that right now. I've been here the last 2-3 days.
"When we get back, we'll find out what the staff makeup is. If it is Josh, I'm really looking forward to working with him. He's a tremendous friend and a great football coach."
McDaniels was New England's offensive coordinator from 2006-08 before becoming head coach of the Denver Broncos in 2009. He was fired with a 3-9 record in 2010 after losing 17 of his last 22 games, but he landed with the St. Louis Rams this season as their offensive coordinator.
The Rams scored the fewest points per game in the NFL (12.1), gained the second-fewest yards (283.6) and the third-fewest passing yards (179.4). Sam Bradford struggled at quarterback with just six touchdown passes and six interceptions in McDaniels' system, which had many more longer-developing pass plays than the Rams had in 2010 under Pat Shurmur.
That lack of production contrasts sharply with the Patriots' offense under McDaniels.
McDaniels, 35, was the only Rams assistant under contract through the 2012 season when coach Steve Spagnuolo was fired Jan. 2.
McDaniels spent time with Patriots coach Bill Belichick this weekend and left New England on Saturday morning to return to St. Louis. Other teams, including the Kansas City Chiefs, wanted to talk with McDaniels, but the source said his sole focus was on the Patriots.
McDaniels' decision to rejoin the Patriots is partly based on family considerations, a source told NFL Network's Albert Breer. After three tumultuous years and two major moves, McDaniels is seeking stability for his wife and young children. New England provides that as a place where McDaniels spent seven years (2001-08) and has a long-standing foundation in place.
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The Associated Press contributed to this report.