The Ducks get back a fourth-round pick in the 2014 NHL Draft which they had previously traded to the Capitals.
"It's a good challenge for me personally," Penner said during a conference call. "I look forward to coming and hopefully adding something that they were looking for to help make the push to the playoffs and compete for the Stanley Cup."
The 31-year-old, who can become an unrestricted free agent on July 1, said he hopes to be in the lineup when the Capitals visit the Philadelphia Flyers on Wednesday night and added that he had no indication he was about to be traded.
Penner has 13 goals and 32 points in 49 games this season, his first back with Anaheim. He began his career with the Ducks in 2005-06 and won the Stanley Cup with them the following season before signing an offer sheet with the Edmonton Oilers which the Ducks elected not to match. Penner had a career-high 32 goals and 63 points with the Oilers during the 2009-10 season but was traded to the Los Angeles Kings at the 2011 NHL Trade Deadline. The following year he won his second Stanley Cup.
Penner has 150 goals and 307 points in 571 regular-season games. He has 13 goals and 35 points in 78 Stanley Cup Playoff games.
He's familiar with at least one of his new teammates; Penner and Washington forward Eric Fehr both come from Winkler, Manitoba.
"He grew up playing hockey with my older brother," Fehr said of Penner. "Obviously, I've seen him play a lot. When their team was short a few players I'd get called up and played with my brother and with Dustin. We kind of grew up together. Obviously he's a few years older, but we kind of grew up playing together."
At 6-foot-4, 247 pounds, Penner should provide size as well as some scoring ability.
"He's a really big guy who has proven he can score and he can play on pretty much any line on our team," Fehr said. "I'm not exactly sure where he'll be fitting in once he gets here, but he can bring just about anything to the table."