[3] Having gone undrafted into the National Hockey League (NHL), Keeper left the University of Maine to sign an entry-level contract with the Florida Panthers on March 21, 2019.
[2] He spent most of the 2019–20 season with the Panthers' American Hockey League (AHL) affiliate, the Springfield Thunderbirds, scoring 6 goals and 18 points in 61 games.
[6] As a restricted free agent from the Panthers following the Return to Play qualifying series, Keeper was re-signed to a one-year, two-way contract on August 31.
[8] As an unrestricted free agent from the Panthers after completing his third season within the organization, Keeper was signed to a two-year, $1.525 million contract with the Vancouver Canucks on July 28, 2021.
Collectively, Keeper missed three months of the 2023–24 season with an injury to his lower body,[12] limiting him to just 22 games played, scoring one goal and registering four points in that span.