Durnan only played seven seasons in the NHL, but accomplished much in his short career. Durnan was the recipient of the Vezina Trophy as top goaltender in each of his first four seasons, from 1944 to 1947, becoming the first to capture the award in four successive seasons. A poor season by the Montreal Canadiens in 1948 allowed Turk Broda of the Toronto Maple Leafs to end Durnan's streak. However, Durnan returned to prominence the next season, capturing his fifth and sixth Vezina Trophies in 1949 and 1950. Following the 1949-50 NHL season, Durnan abruptly retired, no longer able to stand the stress of playing professional hockey. He later went into coaching, most notably with the Ottawa Senators of the QSHL in 1950-51, and the Kitchener-Waterloo Dutchmen of the OHA in 1958-59.

Durnan set a long-standing modern NHL record between February 26 and March 6, 1949, when he amassed four consecutive shutouts, not allowing a goal over a span of 321 minutes, 21 seconds. This record was not surpassed until 2004, when Brian Boucher, then of the Phoenix Coyotes, broke it.

He was inducted into the Hockey Hall of Fame in 1964. In 383 regular-season games, Durnan had 208 wins, and 112 losses, with 34 shutouts and a 2.36 goals-against average. He had 27 wins, and 12 losses, with 2 shutouts and a 2.07 average in 45 playoff games.

Durnan also won the 1940 Allan Cup with the Kirkland Lake Blue Devils.

Durnan died of kidney failure on October 31rst,1972.He suffered from diabetes in his last years and his health had been failing steadily.