Alex made his hockey debut in 1947-48 with the Fort William Rangers of the Thunder Bay Junior Hockey League playing in just one game during that season. The next year he played 12 games racking up 16 goals, 8 assists and a league leading 53 penalty minutes. Alex continued with the Rangers until the 1950-51 season when he was moved to the Oshawa Generals of the OHA-Jr, where he led the league in assists with 72. That same year the Detroit Red Wings were headed for the playoffs and Jack Adams wanted to give some of his players a rest before the gruelling playoffs began, so Alex was called up for a 1 game trial. Delvecchio began the 1951-52 season with the Indianapolis Capitols, where after 6 games he was called up to the Red Wings for the remainder of his career. That year Alex had his name inscribed on the Stanley Cup for the first of 3 times. Alex remains to this day one of the few players to have played his entire career with the same team…a career that lasted for 24 active playing seasons in the NHL.

Alex began his career by centering Metro Prystai and Johnny Wilson. In 1952-53 he replaced Sid Abel on the famed "Production Line" centering Gordie Howe and Ted Lindsay. Delvecchio was referred to by Paul Chandler of the Detroit News as a playmaker and a planner, because of his ability to read the situation and take full advantage of it. By 1954-55 Alex had his named inscribed for the final time on the Stanley Cup.

In 1956-57 Alex suffered his only major injury by twisting his ankle which caused him to sit out 22 games. Over the balance of his career he only missed 21 games, making him one of the most durable players in the league. For the next couple of seasons Alex honed his skills and in 1959 he won the first of 3 Lady Byng Trophies.

Delvecchio was a quiet leader in the dressing room and led the team by example, and his team mates voted him team captain in 1962, an honour he held until his retirement.

In 1966 Alex led the league in playoff assists and won his second Lady Byng Trophy. There were rumours floating around the league that Alex was going to be traded to the Toronto Maple Leafs, but then coach, Punch Imlach stated, "We don't want any Lady Byng winners in Toronto," which suited Delvecchio just fine.

In 1968 the Red Wings acquired Frank Mahovlich from Toronto. Alex centred Frank and Gordie Howe forming one of the most potent scoring lines in NHL history. In 1968-69 season they scored 118 goals breaking the then record set by Toe Blake, Elmer Lach and Maurice Richard of the Montreal Canadiens back in the 1940's. There success was shortlived as Frank was later traded to the Canadiens in 1971.

By this time Alex was in the latter stages of his career, but like all great "supporting actors", Alex was still an integral part of the Red Wings. On October 30, 1970, Alex wrestled the puck from the Bruin's great, Bobby Orr to score his 400th goal. Later in the same game Alex scored his second goal on Gordie Howe's 1000th assist. Delvecchio also set up Howe's 700th goal, and yet another Howe goal brought Delvecchio's assist total to 1000. Alex noted that it was great to play with better players because it helped you to elevate your game as well.

Alex's career wound down in the 1973-74 season when he played just 11 games with club before becoming head coach for the remainder of that season and the next.

Before leaving the game Alex was voted to the NHL Second All Star team twice, once as a centre and once as a left winger, making him one of only 3 players to have done so up to that point. Dit Clapper and Sid Abel were the only other two players to have reached that milestone. Alex won the Lady Byng in 195, 1966 and 1969 and later won the Lester Patrick Trophy in 1974. Rounding out his career were 13 All Star Game appearances.

When his career was over, Alex was second only to Gordie Howe in games played(1,549), assists(825) and points(1,281). Alex was only the second player in league history to play more than 20 seasons with the same team, again second only to Gordie Howe. In 1977, Alex was inducted into the Hockey Hall of Fame, and in 1991 his number 10 was retired by the Detroit Red Wings.