The Nationals announced the deal Friday.
Roenicke has appeared in 190 games over six seasons with Cincinnati, Toronto, Colorado and Minnesota. He pitched in 63 games with the Twins last year, going 3-1 with a 4.35 ERA and one save.
He is the brother-in-law of Nationals shortstop Ian Desmond. Desmond welcomed Roenicke to the team by tweeting: ''Can't beat em' join em'.''