Marquis, 31, is coming off one of his best seasons, going 15-13 with a 4.04 ERA with the Rockies. He also represented Colorado in the All-Star Game.
During his 10-year career -- which has included stints with the Braves, Cardinals, Cubs and Rockies -- Marquis has won 94 games with a 4.48 ERA.
Marquis will help a staff that ranked 16th in the National League in ERA (5.00). He is expected to be the No. 2 starter behind John Lannan and be a mentor to the young staff, which also includes Craig Stammen and J.D. Martin.
Marquis said last week he can be one player who can help Washington's inexperienced staff. Marquis indicated that he can teach the younger pitchers what he learned from veterans like Tom Glavine, Greg Maddux, Chris Carpenter and Matt Morris.
In fact, Marquis felt he was a mentor to Rockies hurlers Jorge De La Rosa and Ubaldo Jimenez.
"Learning from those veterans, learning how to win and recognizing situations, I felt I brought that to the table in Colorado and I really helped ... De La Rosa and Jimenez, who were trying to get over that hump," said Marquis. "I feel I could bring that [kind of leadership] to a team."
Marquis also has a connection to team president Stan Kasten and assistant general manager Roy Clark. Both Kasten and Clark were with the Braves when they drafted Marquis in 1996.
Marquis said being familiar with people on the Nationals is huge.
"The comfort factor with people in the organization makes the transition easier," he said. "It's nice to have familiarity."
Published reports surfaced that Marquis, who is a New York native, wanted to play for the Mets, but he said he wants to play for a team that makes him feel wanted.
"I want to play for a team that is headed in the right direction and making the moves that is necessary to get themselves back to being a winning organization," Marquis said. "Some of the moves the Nationals have made -- like [signing Stephen Strasburg] signing Pudge [Ivan Rodriguez] and getting [reliever Brian Bruney] -- they are making the necessary steps.
"I feel I can fit right in and bring a winning attitude to the team. Every where I've been, I've won. I feel it's not a coincidence. I want to help a team get over the hump."