On March 30, 2012, Tennyson, a native of Pleasanton, California, signed a two-year entry-level contract with his hometown San Jose Sharks.

On July 1, 2017, Tennyson was on the move as a free agent, agreeing to a two-year contract with the final year on a one-way basis with the Buffalo Sabres.

On July 1, 2019, Tennyson left the Sabres as a free agent to sign a two-year, two-way contract with the New Jersey Devils.

He played the majority of the season with AHL affiliate, the Milwaukee Admirals, adding a veteran presence to the blueline in 53 games.

[11] On January 30, 2024, it was announced via Instagram that Tennyson would be joining the Coachella Valley Firebirds broadcast team as an analyst and brand ambassador,[12] effectively ending his playing career.