[6] Gardner joined the North Dakota Fighting Hawks as a freshman for their 2015–16 season, where he helped them win their first NCAA Championship title in 16 years.

[2] In January 2016, Gardner was named National Collegiate Hockey Conference (NCHC) Rookie of the Week after scored four goals over two games.

[14] Gardner was invited to participate in the Dallas Stars' 2019 training camp prior to the start of the 2019–20 season but was re-assigned to the AHL on September 17.

[16] Gardner made his NHL debut on October 5 against the St. Louis Blues, logging four faceoff wins and one hit in 12:04 time on ice.

[17] Upon joining the Dallas Stars, he records his first career NHL assist in a 2–1 shootout win over the Columbus Blue Jackets on March 14.

[20] On July 1, 2023, Gardner left the Stars organization as a free agent in signing a two-year, two-way contract with the Philadelphia Flyers.