Buono spokesman David Turner said he could not comment on whether Buono had picked Silva.
The selection was first reported Thursday afternoon by the political website PolitickerNJ.
Buono will officially announce her pick at a news conference Monday morning in East Rutherford, Turner said.
A call placed to Silva at the New Jersey SEIU 1199 office was directed to Turner.
Buono's pick of Silva is unlikely to change the outcome of the race - a recent Quinnipiac poll showed Christie leading Buono by a 2-1 ratio - but represents an attempt by the Middlesex County Democrat to draw a sharper contrast with Christie, said Patrick Murray, a pollster at Monmouth University.
"She wants to point out he's not as moderate as he says he is," particularly on women's health care and the minimum wage, Murray said. Silva has been an advocate for workers, speaking out against state budget cuts affecting nursing homes.
According to a 2005 article in the Passaic Herald News, Silva's mother moved from Puerto Rico to the Bronx, where Silva was raised in public housing. While in college, she began advocating for workers through a New York chapter of ACORN, according to the article.
Silva's selection also signals Buono's "thumbing her nose" at Democratic Party leaders who endorsed Christie, Murray said.
She is saying, "You make it tough for a woman to rise in the ranks for this party," he said.
A two-woman ticket "does make a statement," he said.
Until 2009, New Jersey gubernatorial candidates did not have running mates. Christie's lieutenant governor, Kim Guadagno, is the first to hold the position.
State Sen. Raymond Lesniak (D., Union) said Silva would be "an excellent choice."
Silva would bring "a lot to the ticket," with experience "not only in the labor movement, but her support of women's issues that are so important to the people in the state of New Jersey," Lesniak said.
Buono previously named Silva as a campaign cochair. Silva appeared with Buono and the four Democratic candidates for U.S. Senate at a news conference on the state's foreclosure crisis this month in Newark.
Contact Maddie Hanna at 856-779-3232 or firstname.lastname@example.org, or follow on Twitter @maddiehanna.