A physical forward known for his fighting ability while with the Maroons and Rangers, an apparent decline in his play was reversed when he switched to defence after he was traded to the Bruins.

Siebert was named an all-star three times after the switch and won the Hart Trophy as the NHL's most valuable player in 1937 as a member of the Canadiens.

Born in Plattsville, Ontario, Siebert grew up in the nearby community of Zurich, located on the eastern shores of Lake Huron.

[4] He won the Ontario Hockey Association (OHA) and eastern Canadian junior championships with Kitchener in 1922–23, but lost the Memorial Cup final to the University of Manitoba.

[2] His physical style of play occasionally resulted in Siebert being brought in front of league president Frank Calder for supplementary discipline, as in December 1927 when he was suspended for a time following a violent melee with Billy Boucher of the New York Americans.

[10] After Eddie Shore was suspended for his assault on Ace Bailey, Bruins coach Art Ross shifted Siebert from left wing to defence.

[12] He later scoffed at the legend of his comeback in Boston, stating that he never lost his ability to play at the same level he did with the Maroons, instead blaming Lester Patrick for improperly utilizing him in New York.

[1] Though he was named a first team all-star in 1935–36,[3] the Bruins decided Siebert's career was in decline and chose to trade him to the Montreal Canadiens along with Roger Jenkins in exchange for Leroy Goldsworthy, Sammy McManus and cash following the season.

On August 25, 1939, while vacationing with his family and swimming with his daughters at Lake Huron, he drowned attempting to retrieve an inflatable tire they were playing with.

[2] Shocked by the news, Siebert's peers lauded his character and play, indicating that his death was a considerable loss to the game of hockey.

Among them, his former manager with the Maroons, Tommy Gorman, remarked that Siebert was popular with his fellow players and was a great defenceman who "lost fairly and won modestly".

[11] His loss represented a significant financial burden for his family as he spent nearly all of his income paying for his paraplegic wife's medical costs.