Mayer made the jump from amateur hockey with the Lake Placid Roamers to junior ice hockey in 1949. He was the goalie of the Barrie Flyers who lost the Eastern Canada championship final series 5-4 to the Montreal Royals, in April 1949 for the George Richardson Memorial Trophy. He began his Professional hockey career in 1949 with the Pittsburgh Hornets.
Gil stood 5'6" and weighed between 128 and 135 pounds during his career.He was "nicknamed "The Needle".
In the 1951-1952 season Mayer wore # 0 because he was so hard to score against with 5 shutouts and a Goals Against Average (GAA) of 2.57 for the Pittsburgh Hornets. Mayer was selected to the AHL all-star team for the 1950-1951 season and consecutively from the 1952-1953 season through the 1954-1955 season. The same year he won a league title, a $300 bonus, and captured goalie honors with a 3.25 goals against average. He allowed 146 goals in 52 games. During his career he was on 3 Calder cup winning teams; 2 with the Pittsburgh Hornets and 1 with the Hershey Bears.
Gil won the AHL "Hap" Holmes Award (goaltender with the lowest GAA) 5 times. This is a 1st all-time record. Mayer was 2nd all time in AHL Regular Season Play in the following categories: 14 seasons, 680 games, 346 wins, 41 shutouts. He was also 2nd all time in AHL Playoffs in these categories: 80 games, 50 wins, 6 shutouts.
His lifetime GAA during regular season play was 2.89. His lifetime GAA in playoff action was 2.27.
Early in the second period of Pittsburgh's game against the Syracuse Warriors, on February 6, 1952, Mayer was cut by a puck which struck his face. His nose hemorrhaged but he returned to the ice after thirty minutes. The Warriors triumphed 4-2 in a contest in which Mayer made several stellar saves. The deciding goal, in front of a crowd of 1,534 at Memorial Auditorium in Syracuse, New York, was quite lucky. Kelly Burnett made a baseball swing at a high-flying hard-hit puck and knocked it 18 feet, still in the air, past Mayer.
Mayer shut out the Springfield Indians on March 22, 1955, in the first round of the AHL playoffs. The Hornets benefited from goals by Bob Hassard and Jack Caffery.
He was traded to the Hershey Bears on July 5, 1956. The Bears also obtained from Pittsburgh defenceman Jack Price, centre (ice hockey) Willie Marshall, centre (ice hockey) Bob Hassard, and forward (ice hockey) Bobby Solinger.
As goalie of the Cleveland Barons he sustained a broken jaw and missed three weeks of competition in 1959. He was hit by a slapshot during practice which required four sutures. His jaw was set at Lakewood Hospital in Cleveland. He was replaced by Don Rigazio, a goalie for the 1956 U.S. Olympic Team.
In 1959 Mayer became the first goalie in the AHL to wear a Goalie mask. He was joined in 1960 by Gerry McNeil of the Quebec Aces.
Trainer Les Binkley replaced Mayer after he was hit behind the ear with a puck in a Barons' loss to the Buffalo Bisons on October 30, 1960. Binkley ceded all three Bisons' goals, playing all the way after the fifth minute.
Mayer made his NHL debut with the Toronto Maple Leafs against the Detroit Red Wings on December 1, 1949, after being called up from the Hornets. Toronto's regular goalie, Turk Broda, was suspended for weighing 197 pounds. He had a weight limit of 190 pounds. Broda, 35, was the oldest active NHL goalie at the time.
Mayer had a natural weight of 128 pounds but tipped the scales at 166 pounds wearing all of his equipment. The 38 pounds of steel, wood, leather and wool costs $300 and required 30 minutes for dressing and removal.
On October 21, 1954, Mayer was brought up from Pittsburgh to substitute for injured Toronto goalie Harry Lumley. As a replacement Mayer was all that could be asked and he was given practically faultless support by his fast-skating mates. The Leafs surprised a Montreal crowd of 14,004 by defeating the Montreal Canadiens, 3-1, in a game which Harry Watson scored his 200th career goal.
During a Toronto losing streak Mayer conceded a late first-period goal to Ed Litzenberger of the Chicago Black Hawks on February 5, 1956. The shot from along the boards hit Mayer's pads and dribbled into the far corner of the net. It proved to be the winning tally in a 3-2 victory and the fourth loss in a row for the Maple Leafs.
Mayer's last season of professional hockey came during the 1962-63 season, playing in the American Hockey League for the Providence Reds.
Mayer died at the age of 86 on September 29, 2015.
NHL totals: Toronto Maple Leafs
(1949 - 1950) (G) 1 (GA) 2 (GAA) 2.00 (Svs) 0.00
(1953 - 1954) (G) 1 (GA) 0 (GAA) 0.00 (Svs) 0.00
(1954 - 1955) (G) 1 (GA) 0 (GAA) 0.00 (Svs) 0.00
(1955 - 1956) (G) 6 (GA)19 (GAA) 3.17 (Svs) 0.00