The Thunder Bay Junior A Hockey League (TBJHL) was a Canadian junior ice hockey league that existed from c. 1920 to 1980. The TBJHL operated in Northwestern Ontario, primarily in the Thunder Bay region.

The Thunder Bay Junior A Hockey League was what is now known as a Major Junior hockey league from roughly 1920 until the Canadian Amateur Hockey Association realignment of 1970. After 1970, the TBJHL was relegated to Tier II Junior A and competed for the Manitoba Centennial Trophy until the league folded in 1980.

Thunder Bay and the TBJHL was considered on the border region of what people would call Eastern Canada and Western Canada. Due to its location, the Thunder Bay league often switched from East to West year-to-year in National playdowns. The league's remoteness resulted in keeping the league's few teams from competing in the neighbouring Manitoba Junior Hockey League or Northern Ontario Junior Hockey League, making the league's existence a necessity to the region's hockey community.

Thunder Bay Junior A Hockey League teams made the Memorial Cup finals four times in fifty years, winning Canada's top junior hockey prize in 1922 (Fort William War Veterans) and 1948 (Port Arthur West End Bruins).

The TBJHL is the indirect predecessor of the Superior International Junior Hockey League who brought a Junior A league back to the region in 2001, 21 years after the TBJHL folded.

Although hockey in Thunder Bay dates back well before 1920, the Thunder Bay Junior Hockey League first competed in Memorial Cup action in 1921. In only their second year of operation at the Junior A level, the league celebrated their first National championship as the Fort William War Veterans defeated the Regina Pats 5-4 and tied them 3–3 to win the championship. To get there, the Vets had to defeat Toronto Aura Lee in the Eastern Canada final, beating them 5–3 in a one-game showdown.

It took 26 years for a team from the Thunder Bay Junior A Hockey League to repeat the feat. In 1947–48, the Port Arthur West End Bruins finished the regular season in first place with a record of 9 wins, no losses, no ties. They were given a berth directly into the league final where they met the Fort William Columbus Canadiens. The first game resulted in a 7–7 tie, and the Bruins won the second game 9–7. Game three sparked some controversy as the game was tied 5-5 and the Columbus Canadiens walked off the ice. In response, the league ruled the game a forfeit in the Bruins favour. Games four and five were won by the Bruins 8-3 and 5–3 to give the series and league championship to the Bruins 4-games-to-none with 1 tie. In the Eastern Canadian semi-final, the Bruins had to play the Manitoba Junior Hockey League's Winnipeg Monarchs. Port Arthur won game one 12–3, game two 6–4, and game three 10–4. The Monarchs started to rally, winning game four 7-5 and game five 5–3. Finally, in game six, the Bruins were able to put the final nail in the coffin as they won 7-2 and took the series 4-games-to-2. Next, Port Arthur found themselves in the Abbott Cup final against the Southern Alberta Junior Hockey League's Lethbridge Native Sons. Lethbridge took game one 6-1 and game two 7–6. Port Arthur came back with a 7–4 win. Lethbridge put the series on the brink with a 5–4 win before Port Arthur came back with three solid victories; 5–0, 6–4, 11–1; to come from behind and take the Abbott Cup. This earned them a berth in the Memorial Cup against the Ontario Hockey Association's Barrie Flyers in Toronto. Ignited by the Abbott Cup final comeback, the Bruins kept on rolling, sweeping the Flyers 4-games-to-none with scores of 10–8, 8–1, 5–4, and 9-8 respectively. This would be the final Memorial Cup won by a TBJHL team.

From the 1964 until 1969, the TBJHL had a rivalry and was in direct competition annually for the TBAHA seed to the Memorial Cup against the neighbouring Northwestern Ontario Junior Hockey League. By 1969, the NWOJHL had dropped to Junior B and may have become the Thunder Bay Junior B Hockey League, the TBJHL's feeder league in the 1970s.