Williams was 8, having met WTT co-founder Billie Jean King at a clinic in Long Beach, Calif. At 17, Roddick played for the Idaho Sneakers.
Now they're part owners of King's summer league that began in the 1970s and features men and women professional players in eight cities. WTT announced Monday that Williams and Roddick will join majority owner King and a group of four other part owners that includes the U.S. Tennis Association.
"It's important to have the younger generation involved in our strategic planning," King told The Associated Press by phone. "We feel these two are exceptional human beings not just on the court but off the court."
Roddick, who retired from tennis after the U.S. Open, is looking to start a team in 2014 near his home of Austin, Texas.
"Obviously, it's never a bad thing to stand beside Billie Jean King in any venture," he said.
He and Williams will still play for their WTT teams during the July 7-28 season. Williams leads the two-time defending champion Washington Kastles; Roddick will play for the Lasers of Springfield, Mo.
The former top-ranked players will help identify new markets and reach out to potential owners, sponsors, fans and players. The league this season added a new title sponsor, the pharmaceutical company Mylan; moved its Kansas City, Mo., team to Irving, Texas; and plans to expand to 16 teams by 2018, WTT Commissioner Ilana Kloss said.
"I believe in Billie and Ilana's vision for tennis," Williams said by phone from the Madrid Open. "For us to continue to grow the sport, we have to be more inventive. We have to capture the attention of fans and capture the attention of young people."
In 2009, the USTA became a 25 percent owner of the league in an effort to expand the USTA Junior Team Tennis program. The WTT's kid-friendly atmosphere helps introduce them to the sport with mascots, coaches, cheerleaders and music between games. Free rackets are offered at the clinics.
Williams said her entire family went to the clinic hosted by the tennis great at Billie Jean Moffitt King Park.
"I remember wanting to impress her," Williams said. "I was going to show her I was the best kid there. I remember she was pitching balls to us. I guess I thought I was pretty good."
King got free tennis lessons near the park that bears her name in Long Beach, and Williams understands the importance of giving kids a chance to play.
"My parents started me off early, but there were a lot of kids. It was their first time," she said. "That's the way we have to grow the sport and give opportunities to young people who normally wouldn't be able to play the game."
The WTT Eastern Conference features teams in Boston, New York, Philadelphia and Washington. The Western Conference plays in Orange County and Sacramento, Calif.; Springfield, Mo.; and Irving, Texas.
Kloss said the league is looking at potential teams in Austin, Chicago, Denver, Seattle, Toronto and Vancouver, British Columbia. Roddick considers Austin and several cities in Texas a good fit, especially since tennis has become more global, with some U.S. tournaments moving to other countries.
"Davis Cup did very well there," Roddick said. "Tennis has always done pretty well in Texas. Whether that's in Austin, San Antonio, Dallas, there's plenty of opportunity in Texas right now."
Roddick said playing for the Sneakers helped him transition from No. 1 in the juniors to the professional ranks.
"You always hear about this massive divide between junior tennis and pro tennis," said Roddick, who recalled playing James Blake and breaking a racket. "WTT provided me with 13-to-14 matches in a 20-day schedule.
"So by the time I got to (ATP) tour events that summer, I'd already been playing against guys ranked 200 in the world consistently. It was unbelievable exposure for me."
Sloane Stephens will play for the Philadelphia Freedoms this summer. The 20-year-old joined WTT in 2009 as an amateur and shot up in the rankings after beating Serena Williams at the Australian Open in January.
"The great thing about WTT is we can build more stars," Kloss said. "Our sport tends to be very marquee-driven. The beauty of WTT is that you really do build local stars in these communities and the communities come out to see their players."
The 30-year-old Roddick plans to use social media to help drive interest to the teams and league. He has 1.1 million followers on Twitter.
"It certainly was beneficial for me as far as a Twitter following the last couple years of my career," he said. "I don't see why it can't be that way in WTT. You need a running dialogue of what's going on."
Roddick has stayed busy since his retirement in September, working to open an education center next year in Austin -- with King as a board member -- and joining Athlete Ally to fight homophobia in sports.
King is pleased to have Williams and Roddick for the next phase of WTT.
"They believe in community," King said. "It's obvious with Andy and Venus that they care about young people. They want to make a difference off the court."