Financial terms of the deal were not disclosed but Powell, 29, earned $1.6 million last season and was expected to secure a deal worth $3 million per year.
"The addition of Jay Powell gives us another important piece to our bullpen," said Hart, who took over less than two months ago. "He has enjoyed success pitching late in games and is able to take the ball 70 or more times a year."
Powell split last season between the Houston Astros and Colorado Rockies and went 5-3 with a 3.24 ERA and seven saves in 74 relief appearances. He went 3-1 with a 2.79 ERA in 39 outings for the Rockies and even served as their closer down the stretch.
In parts of seven seasons with the Florida Marlins and Houston Astros, Powell has a lifetime record of 29-20 with a 3.81 ERA and 22 saves. He was a member of the world champion Marlins in 1997 and participated in the postseason with the Astros in 1998 and 1999.
With Texas, Powell could set up Jeff Zimmerman or even share the closing duties. With the signing earlier this month of Todd Van Poppel, Rangers manager Jerry Narron now has some flexibility in his bullpen -- something he sorely lacked last season.
"I think the bullpen was a hole last season and we have tried to do some things (this offseason)," Hart said. "It was an area that needed to be addressed and I think we have made it more competitive. Not perfect, but it is more competitive."