The Rangers sent infielder Chris Bostick and right-hander Abel De Los Santos to Washington in exchange for the former first-round draft pick.
The Rangers plan on giving Detwiler an opportunity to earn a spot on the starting rotation. As it stands, Yu Darvish, Derek Holland and Colby Lewis are in the rotation with the club trying to add a veteran starter and promote one of their minor league prospects to fill out the staff.
"I don't really look at it as them giving me up. I look at it as the Rangers really wanting me, and they were willing to give up some of their prospects for me," Detwiler said. "I think it's going to be a better fit for me. ... I didn't really see myself in a relieving role. I think I am a starter. I'm just ecstatic to get another chance to start somewhere."
Last season, Detwiler pitched in 47 games as a reliever, compiling a 4.00 ERA in 63 innings with a WHIP of 1.413 and a 1.86 strikeout/walk ratio.
"We got him with the intent to use him in the rotation," general manager Jon Daniels said. "It's well-documented he wants to start. When you've got a player that's motivated and maybe has some internal drive, internal motivation to go out there and perform, it's usually a good thing."
While Daniels likes the internal options for the fifth spot, he said there will always be more conversations about adding starting depth.
"I do feel this does take the edge off a little bit in that we feel like Ross can come in and give us some innings as a starter," he said.
Detwiler has started 69 of his 132 major league games, all with the Nationals, who took him with the sixth pick in the 2007 draft. He has a career record of 20-32 with a 3.82 ERA.
Bostick was at High-A Myrtle Beach last season, while De Los Santos made 41 combined appearances for Myrtle Beach and Class-A Hickory.
With the signing, the Rangers currently have filled the 40-man roster, but GM Jon Daniels said before the trade he plans on adding a right-handed reliever early next week.
Calvin Watkins of ESPNDallas.com contributed to this report.