The Murrayfield-based ice hockey outfit made their move following the recent departures of star men Ryan Hayes and David Rutherford. Thompson, 25, played for Rochester Institute of Technology last season.
Player-coach Riley Emmerson said: “Brandon is a good two-way player. He is a fantastic, smooth skater who plays with an edge. Trevor Gerling and Brandon were team-mates in the past and I am excited to add him so quickly after losing the two players last week.
“We have a tough weekend ahead but. if our guys show the passion, pride and determination we showed last weekend we will get back to winning games.”
Thompson said: “It has all happened so fast, but I am looking forward to the opportunity and playing in Edinburgh. I have been skating on a regular basis and cannot wait to get back playing at the weekend.”
Caps face two games this weekend, away to Fife Flyers on Saturday (7.15pm) and Braehead Clan at home (Sunday, 5.30pm).