Earlier in his career, he served as a law clerk to Judge J. Michael Luttig of the United States Court of Appeals for the Fourth Circuit and then to Justice Anthony Kennedy of the Supreme Court of the United States.

[3] Democrats on the committee opposed Nielson over his role in defending California's Proposition 8 and his role in reviewing two torture memos in 2004 and 2006 when he was serving as a deputy assistant general at the Office of Legal Counsel for the Justice Department.

[4] On March 6, 2018, Illinois Senator Tammy Duckworth put a hold on his nomination.

[5] On January 3, 2019, his nomination was returned to the President under Rule XXXI, Paragraph 6 of the United States Senate.

On January 23, 2019, President Trump announced his intent to renominate Nielson for a federal judgeship.