[4] After graduation, Newsom served as a law clerk to Judge Diarmuid O'Scannlain of the United States Court of Appeals for the Ninth Circuit.

[9] Afterwards, Newsom was a partner at Bradley Arant Boult Cummings LLP in Birmingham, where his practice focused on appellate law.

[13][14] On May 8, 2017, President Donald Trump nominated Newsom to a seat on the United States Court of Appeals for the Eleventh Circuit vacated by Judge Joel Fredrick Dubina, who assumed senior status on October 26, 2013.

[23] In June 2020, Newsom wrote for the divided panel when it vacated a lower court's injunction ordering the Miami-Dade County Corrections and Rehabilitation Department to enforce social distancing and take other preventative measures to protect prisoners from COVID-19.

[24][25] On May 23, 2022, Newsom, joined by Tjoflat and Ed Carnes, ruled in Moody v. NetChoice that several provisions of Florida's social media moderation law were unconstitutional, but several others were constitutional.