Bossie had been tapped to lead the legal effort as Trump has refused to concede the election to President-elect Joe Biden, the president's Democratic rival.
Mr. Lewandowski had been in Philadelphia for days since attending the event, and believes he may have contracted it there, the person said.
Lewandowski, a political strategist and founder of Lewandowski Strategic Advisors, served as Trump's campaign manager for part of his 2016 presidential race.
According to the Post, RNC officials said the committee was contact tracing individual cases, but many staffers are still undergoing testing.
Asked if he was experiencing symptoms of the virus, Lewandowski told CNBC: "I feel great". Several prominent members of President Trump's team have tested positive for the virus, despite repeated claims from the administration that everything is under control.
The late September event announcing Justice Amy Coney Barrett as Trump's Supreme Court pick was dubbed a superspreader after Trump, first lady Melania Trump, Sen.