Apps was a strong athlete, six feet tall, weighing 185 pounds, and won the gold medal at the 1934 British Empire Games in the pole vault competition. Two years later he represented Canada at the 1936 Olympics in Berlin, Germany, where he placed sixth in the pole vault event. After watching him play football at McMaster University, Conn Smythe signed Apps to play hockey with the Toronto Maple Leafs.

Apps played centre position with the Toronto Maple Leafs for his entire professional hockey career. His jersey number was 10. He was the winner of the first Calder Memorial Trophy in 1937, and the 1942 Lady Byng Memorial Trophy. Apps served as the Maple Leafs captain during the first National Hockey League All-Star Game October 13, 1947, at Maple Leaf Gardens. He also played for an all-star team competing in Montreal on October 29, 1939, to raise money for Babe Siebert's family.

Apps was in the prime of his career when he joined the Canadian Army during World War II at the end of the 1943 season. He served two years until the war was over, whereupon he returned to captain the Leafs, winning 2 more Stanley Cups in 1947 and 1948.^[3]

Apps contemplated retirement following the 1947 Stanley Cup win, but returned in order to reach the 200 career goals milestone. With 196 career goals heading into the final weekend of the regular season, Apps scored 5 goals in the two weekend games to surpass his goal.^[4] Despite scoring 53 points in 55 games and setting a career high in goals, Apps retired from the NHL at the age of 33 and took a marketing job with the Simpson's department store. At the same time, he also served as the Ontario Athletic Commissioner.

While still playing hockey, Apps ran for parliament in the 1940 federal election. He was a candidate in the riding of Brant for the National Government Party but lost to incumbent George Wood of the Liberals by 138 votes.

Apps was a Progressive Conservative member of the Legislative Assembly of Ontario from 1963 to 1975. He represented the riding of Kingston from 1963 to 1967 and Kingston and the Islands from 1967 to 1975. He served as the Minister of Correctional Services from 1971 to 1974.

On December 24, 1998, Apps died from a heart attack and was buried in Mountview Cemetery in Cambridge, Ontario. After his death, the Maple Leafs honoured his jersey number and George Armstrong's number, who both wore the number 10. Their numbers were not retired, as the Maple Leafs had a policy of only retiring numbers for players "who have made a significant contribution to the Toronto Maple Leaf Hockey Club and have experienced a career-ending incident while a member of the Maple Leaf team". However, this policy was changed for the Maple Leafs' centennial season, with Apps' number, along with 15 others, officially being retired on October 15, 2016.

Apps was known for his athleticism, character, skating and play-making abilities (alongside a scoring touch, six times reaching the 20 goal plateau).^[4] He has been praised by Maple Leafs alumni, authors, historians and even competitors. Maple Leafs owner Conn Smythe called Apps the greatest player in franchise history, with teammate Howie Meeker noting his strong, consistent play. Ted Kennedy often spoke of his character. Jack Adams, famous for his managerial roles with the Detroit Red Wings, stated that Apps was the greatest centre he had ever seen. Boston Bruins legend Milt Schmidt called Apps the greatest player he ever played against, as did Ted Lindsay in relation to the centre position and gentlemanly characteristics.^[4]

In 1975, he was elected to Canada's Sports Hall of Fame and two years later Apps was made a Member of the Order of Canada.

Several institutions are named for him, including the Syl and Molly Apps Research Centre in Kingston, Ontario, and the Syl Apps Youth Centre in Oakville, Ontario. The sports arena in his home town of Paris is named the Syl Apps Community Centre.

In 1997, Syl Apps was inducted into the Ontario Sports Hall of Fame.^[5] Unveiled by the Ontario Sports Hall of Fame on January 13, 1998, the Syl Apps Award is emblematic of Ontario's Athlete of the Year.^[6]

In 2001, Canada Post included Apps in a series of NHL All-Star 47-cent postage stamps.

The National Hockey League itself listed Apps as one of the 100 Greatest Players to ever play in the league as part of the league's centennial celebrations in 2017.^[4]

Apps and wife Mary Josephine had five children, Joanne, Robert, Carol, Janet and son Syl Apps Jr. (the latter also played the NHL). His granddaughter (and daughter of Syl Jr.) Gillian Apps won the gold medal in the 2006 Winter Olympics, the 2010 Winter Olympics, and the 2014 Winter Olympics for Canada's women's ice hockey team, and his grandson Syl Apps III was a college hockey star at Princeton University and played four years in the minor leagues. His grandson Darren Barber won a gold medal at the 1992 Barcelona Olympics in the men's 8 in rowing. Barber is now a family doctor in Peterborough, Ontario.^[7]

• Calder Memorial Trophy winner in 1937.
• Selected to the NHL Second All-Star Team in 1938, 1941, and 1943.
• Selected to the NHL First All-Star Team in 1939, and 1942.
• Lady Byng Memorial Trophy winner in 1942.
• Stanley Cup champion in 1942, 1947, and 1948.
• Inducted into the Hockey Hall of Fame in 1961.
• Inducted into Canada's Sports Hall of Fame in 1975.
• In 1998, he was ranked number 33 on The Hockey News' list of the 100 Greatest Hockey Players.
• #10 jersey retired by the Toronto Maple Leafs.^[8]
• In January 2017, Apps was part of the first group of players to be named one of the '100 Greatest NHL Players' in history.^[2]