He played college football at Montana State and was signed as an undrafted free agent by the Seattle Seahawks after the 2015 NFL draft.

He had acquired a Canadian passport in October 2015, having qualified for dual citizenship because his mother was born in Toronto.

He was waived during final roster cuts on August 30, 2019,[12] but was re-signed to the team's practice squad the next day.

In Week 4 of 2020 against the San Francisco 49ers on Sunday Night Football, Singleton went into the game on defense due to an injury to T. J. Edwards.

With less than 6 minutes remaining in the game, Singleton recorded his first career interception off a pass thrown by Nick Mullens and returned it for a 30-yard touchdown during the 25–20 win.

[20] After initially playing at the starting linebacker position, he was relegated to backup and replaced by Davion Taylor in Week 6.

[21] In Week 16 against the New York Giants, he caught an interception off a deflection from Rodney McLeod and returned it for a 29-yard touchdown, his second career pick-6.

[23] He was activated one week later on January 10, missing just one game where the Eagles did not play their starters as they had already clinched a playoff spot.

On March 18, 2022, Singleton signed a one-year contract with the Denver Broncos reportedly worth $1.1 million guaranteed with $750k in playing time incentives.

[26] The move reunited him with quarterback Russell Wilson, whom Singleton had formed a relationship with during his short stint in Seattle.

[32] On the opening drive of the Broncos' Week 1 game against the Seattle Seahawks, Singleton intercepted a pass by Geno Smith.