The 23-year-old was acquired July 31, 2009 from the Florida Marlins in exchange for Nick Johnson. Thompson never pitched in the majors, but went 5-13 with a 5.65 ERA in 27 between Double-A Harrisburg and Triple-A Syracuse in 2010. He was impressive in spring training, sparking some thought he might be in the majors in the near future, but couldn't put it together in the minors. In six minor league seasons, Thompson was 27-50 with a 4.31 ERA in 128 games, all but one of them starts.
Losing Thompson gets the Nats' roster back down to the 40-man maximum.
Ironically, the Pirates made room for Thompson by cutting ties with an ex-Washington pitcher. Lefty Wil Ledezma, who pitched for the Nationals in 2009, was designated for assignment to accommodate Thompson on Pittsburgh's 40-man roster.