The one-year deal is worth $5 million and includes a 2016 mutual option, according to Rosenthal. The contract will also include an option buyout.
Janssen, 33, has played all eight of his MLB seasons with the Toronto Blue Jays. Over the last three seasons, he earned 81 saves, including a career-high 34 in 2013.
in 2014, Janssen finished with 25 saves and a 3.94 ERA in 50 appearances. He made $4 million last season with Toronto.
Coming off a 96-66 season capped by a National League East title, the Nationals have made several changes to their pitching staff this offseason. Earlier this month, the team traded reliever Tyler Clippard and signed former Cy Young winner Max Scherzer.
- Stanley Kay