The 68-year-old McMahon was a major Trump backer during his campaign.
Trump said in a statement that McMahon would help to "bring back our jobs and roll back the burdensome regulations that are hurting our middle class." The SBA has an office in every state and helps with financing and training for small businesses and entrepreneurs.
"Our small businesses are the largest source of job creation in our country," McMahon said in a statement. "I am honored to join the incredibly impressive economic team that President-elect Trump has assembled to ensure that we promote our country's small businesses and help them grow and thrive."
McMahon ran unsuccessfully for U.S. Senate seats in Connecticut twice in 2010 and 2012. She spent nearly $100 million on the two campaigns.
The publicly-traded WWE, which McMahon and husband Vince founded more than 30 years ago, has a market value of about $1.5 billion.