Powell was one of three new investors who were announced on Wednesday, along with businessmen Dennis Bakke and David Donnini.
"We have the opportunity to reinvigorate this city and bring baseball back to a generation of youth who have lost their connection to our nation's pastime," Powell said.
"I'm encouraged by baseball's efforts to diversify its ranks and its reach, and the Washington Baseball Club shares that commitment to making this team accessible to every Washingtonian," he said.
The group, led by Fred Malek and Jeff Zients, includes former Fannie Mae chairman Franklin Raines, America Online founding CEO James Kimsey, lawyer Vernon Jordan and former Washington Redskins player Darrell Green.
"General Powell and I are longtime friends who share a deep commitment to this community and everything it has given us," Malek said.
His group has been working since 1999 to bring baseball to Washington. The Montreal Expos moved to the city this season, changing their nickname to the Nationals.
The franchise was purchased by the other 29 major league teams for $120 million in 2002, and Major League Baseball is expected to get more than $300 million in a sale it hopes to complete during this season.
Nine potential ownership groups have paid a $100,000 deposit to enter the bidding.
Powell retired as secretary of state in January.
"I am thrilled to have a man of General Powell's character and stature involved in the Washington Baseball Club's effort to acquire the Washington Nationals," Washington Mayor Anthony A. Williams said.