From 2018 to 2019 he served as the managing director and General Counsel of Nardello & Co., where he headed the global investigation firm's Atlanta, Georgia, office.

President Trump nominated Grimberg to the seat vacated by Judge Richard W. Story, who assumed senior status on December 1, 2018.

[5] On July 30, 2019, the United States Senate invoked cloture on his nomination by a 72–16 vote.

[8] On November 19, 2020, Grimberg threw out a lawsuit brought by a Trump supporter concerning the 2020 U.S. presidential election.

Grimberg found that the plaintiff asserting fraud and improprieties in the election lacked standing to sue, waited too long after the election to file their case, and otherwise demonstrated "no basis in fact or in law" for blocking certification of Joe Biden's narrow victory over Trump in Georgia.