Born in Montreal, Quebec, he was a three-time Stanley Cup winner, he played 14 NHL seasons, from 1923 to 1937, with all but four games as a Montreal Canadiens player. He was captain for Montreal from 1926 to 1932 and from 1933 to 1936.

Mantha started as a right-winger for the Notre Dame de Grace Juniors in 1918-19 season, before playing for Verdun in the Intermediate Mount Royal Hockey League, Montreal Imperial Tobacco, and Montreal Norther Electric in the Montreal industrial league. He played briefly for the Montreal Nationales in the Quebec league. After scoring four goals in nine games with the Nationales, he was signed by the Montreal Canadiens. The Canadiens started Mantha as a forward, then moved him to right defence, because veterans Sprague Cleghorn and Billy Coutu were aging.

When Cleghorn was traded just before the 1925-26 NHL season, Mantha gained a more prominent role. He scored the first-ever goal in the Boston Gardens on November 20, 1928, leading the Canadiens to a 1-0 win over the Boston Bruins. Mantha was named to the NHL Second All-Star Team in both the 1929-30 and 1930-31 seasons.

In the 1935-36 NHL season, Mantha became the Canadiens' player coach. After a dismal season, the Canadiens fired him. The Boston Bruins were involved in a contract dispute with Eddie Shore, so they signed Mantha at the start of the 1936-37 NHL season -- and gave him Shore's number 2 jersey. Four games into the season, Mantha admitted he could no longer play at a competitive level and retired.

Mantha then worked as a linesman and referee for the AHL and NHL. He then tried coaching the junior league Montreal Concordias, Laval Nationales (1943 to 1945), Verdun Maple Leafs (1945 to 1947), and St. Jerome Eagles (1947 to 1948).

He was inducted into the Hockey Hall of Fame in 1960, and died in Montreal, in August of 1974.

The Georges & Sylvio Mantha Arenas are part of the Complexe Récréatif Gadbois in Montreal and named for him and his brother who also played in the National Hockey League.