He played college football at Michigan State and was selected by the Washington Redskins in the fourth round of the 2017 NFL draft.

Nicholson attended Gateway High School in Monroeville, Pennsylvania, where he starred in football, basketball and track and field.

[8] Throughout training camp, he competed for the job as a backup safety against Will Blackmon, Deshazor Everett, Earl Wolff, Josh Evans, Stefan McClure, and Fish Smithson.

On September 17, 2017, Nicholson earned his first career start and made two solo tackles in the Redskins' 27–20 victory at the Los Angeles Rams in Week 2.

[13] On October 15, 2017, he recorded a season-high six combined tackles and broke up a pass, but left in the second quarter of the Redskins' 26–24 win against the San Francisco 49er after sustaining a concussion.

His concussion occurred in the last 45 seconds of the half after Nicholson attempted to tackle wide receiver Pierre Garcon, but lowered shoulder and took a blow directly to his head that knocked off his helmet and rendered him unconscious.

[20] In week 2 against the Dallas Cowboys, Nicholson recorded his first interception of the season off Dak Prescott and returned it 23 yards as the Redskins lost 31–21.

[29] On November 14, 2019, it was reported that the Loudoun County Sheriff's Office was investigating Nicholson regarding the death of 21 year-old Julia Crabbe.