The left-hander and the club agreed to a five-year, $55-million deal through 2017 that also includes a club option for 2018 according to a source. Harrison passed his physical on Wednesday.
Harrison, who is coming off an All-Star season, was eligible for arbitration and could have been a free agent following the 2014 season.
That won't be the case now for Harrison, 27.
He was the team's Pitcher of the Year last season, winning a career-high 18 games with a 3.29 ERA. He set career highs in wins, ERA, starts, complete games, shutouts, innings pitched and strikeouts. He was the AL Pitcher of the Month for June.
With Harrison locked up long term, the club now has four-fifths of its starting rotation under contract for at least the next four seasons. Derek Holland signed a deal last year that keeps him under contract through 2016 with the club holding options for 2017 and 2018. Alexi Ogando won't be eligible for arbitration until after the 2013 season. Texas also signed Yu Darvish to a six-year deal last year through the 2017 season.
Harrison was in town over the weekend for the club's Fan Fest and talked contract with the club. Harrison said at the time he was hoping something could get done over the weekend but left without a new deal in place.