The Seattle Mariners sent the ace left-hander, and reliever Mark Lowe to the AL West-leading Rangers on Friday for first baseman and former South Carolina standout Justin Smoak and three minor leaguers.
It was the third trade in less than a year for Lee, who can become a free agent after this season. The 2008 AL Cy Young Award winner went 8-3 with a 2.34 ERA in 13 starts for the Mariners, who acquired him from the Philadelphia Phillies in December.
Smoak is one of the top prospects in the majors, but the switch hitter batted only .209 in 70 games for the Rangers this season. Also coming from Texas are right-handers Blake Beavan and Josh Lueke, and infielder Matt Lawson.
The Mariners were expected to contend for the West title this season but quickly fell off the pace. They had lost four in a row before Friday night's game against the New York Yankees and were 16 games out.
Seattle's problems made Lee one of the biggest commodities on the market ahead of the July 31 non-waiver trade deadline, and about a dozen teams were believed to have inquired about the pitcher.
Now, Texas gets a big boost in its quest for its first playoff berth since 1999.
"We haven't won anything yet but we feel like we're in position to put our best foot forward," Rangers general manager Jon Daniels said. "We've always said if we had a chance to improve, we would. We're excited about it."
Lee missed the first month of the season with an abdominal injury but quickly made up for the lost time. He is 5-1 with a 1.76 ERA in his past six starts, earning four of his major league-best five complete games.
Lee, who has just six walks in 103 winnings this year, now will wear a Rangers uniform in Tuesday night's All-Star game in Anaheim.
Also leaving Seattle is Lowe, one of the Mariners' most consistent relievers in recent seasons. Lowe likely is done for the year, following back surgery in June.
Smoak and Beavan are the big pieces coming back to Seattle. Smoak was the Rangers' No. 1 pick in 2008 and Beavan was their No. 1 selection a year earlier. Beavan was 10-5 with a 2.78 ERA in 110 innings for Double-A Frisco this season.