The deal was announced Wednesday and is reportedly worth US$5.7 million.
Brouwer recorded 17 goals and 36 points in 79 games last year with the Chicago Blackhawks.
He was acquired by Washington in a draft-day trade that sent Chicago a first round pick (26th overall) in the 2011 draft.
The six-foot-three, 215-pounder led Chicago and ranked fifth in the NHL with 262 hits.
The Caps have been searching for leadership presence in the locker room and a player who can perform in the playoffs.
He was part of the Blackhawks' Stanley Cup victory in 2010, registering four goals and four assists during their post-season run.
That regular season, he had a career-high 22 goals and 40 points in 69 games.
The Vancouver native was drafted by Chicago in the seventh round of the 2004 draft.