On November 6, 2006, the Texas Rangers announced that Washington had accepted their offer to manage the team replacing Buck Showalter, who was fired a month earlier. Washington beat out four other candidates for the job: Rangers bench coachDon Wakamatsu, then New York Mets third base coach Manny Acta, Nippon Ham Fighters manager Trey Hillman and former Rangers catcher John Russell.
At the beginning of the 2007 season, it was rumored that there was a rift between Washington and Rangers star Mark Teixeira. Asked about it, Washington responded,
A lot of times we make three outs on four or five pitches... I just can't see that late in the game when you're four or five runs down. You're at the point where the starter is out of the game, you're in the middle (of the bullpen), these are the guys you want to get to. I've never asked him (Teixeira) to do it when the closeris in the game. But the middle guys, you want to make 'em throw... He feels like he's going to only get one pitch in that type of situation to do something with. He wants to take advantage of it. I've got no problem with that. But can you guarantee with that one pitch that you're going to do something with it? I don't think any ballplayer on earth can guarantee that. You might pop it up, miss it, roll over it, jam yourself. Then you make one out on one pitch. I want to see him get a pitchers' strike right there.
Teixeira was traded to the Atlanta Braves in July 2007 and had been rumored to have been on the trading block before reports of tensions with Washington, as his agent, Scott Boras, had refused to negotiate a contract extension beyond the 2008 season. Reports also suggested tensions between Washington and catcher Gerald Laird. Questioned about the rumors, Washington conceded that the pressure he put on Laird was "a lot to put on a young kid... (But) that's what we've got. He's got to grow up fast."
On August 6, 2007, Washington was ejected for the first time of his managerial career after arguing with umpire Bill Miller over a called third strike to Michael Young, who also was ejected. On March 17, 2010, Jon Heyman of Sports Illustrated reported that Washington tested positive for cocaine during the 2009 season and has admitted to using cocaine.
Washington would become only the second manager of the Rangers franchise, after Johnny Oates, to take his team to the post-season after winning the AL West in 2010; the team's first division title in 11 years. On October 12, 2010, Washington became the first manager in franchise history to win a playoff series, with a 3–2 victory in the ALDS over the Tampa Bay Rays. On October 22, 2010, Washington's Rangers defeated the New York Yankees in the ALCS in six games, to advance to their first World Series in franchise history, before losing to the San Francisco Giants in five games. He also became the third African American to manage a team into a World Series, joining Cito Gaston, who managed the Toronto Blue Jays to the World Championship in the 1992 and 1993 World Series, and Dusty Baker, who managed the Giants in the 2002 World Series.
Referring to Washington, second baseman Ian Kinsler said: "I just love the way he never holds his emotion back, especially when he's managing. He hangs on every pitch, and it's great to know that your manager is in every single pitch and cares that much." In 2009 his salary was about $750,000. On November 4, 2010, Washington agreed to a two-year contract extension.
On October 15, 2011, Washington managed the Rangers to their second World Series in as many years, when the Rangers defeated the Detroit Tigers in the ALCS. The Rangers eventually lost to the St. Louis Cardinals in 7 games, after twice being one strike away from the title in game 6. On January 30, 2012, Washington agreed to another two-year contract extension. He managed the American League in the 2012 MLB All-Star Game.
On September 2, 2012, Washington earned his 507th win as a manager of the Texas Rangers, passing Johnny Oates for 2nd most wins by a Rangers manager. As of the end of the 2012 season, Washington is 61 wins behind Bobby Valentine for first place in wins.
On August 4, 2013, Washington passed Bobby Valentine for the most wins as a Ranger's manager, at 582.
On April 14, 2014, Washington got ejected for arguing an overturned call against the Seattle Mariners. His team lost 7-1 that day.