The 1920–21 Ottawa Senators season was the club's 36th season of play, fourth season in the NHL, and they were out to defend their 1920 Stanley Cup championship. The club would win the NHL championship and defeat Vancouver in the Stanley Cup Finals to win the club's ninth Stanley Cup.

Regular season

Cy Denneny led the club offensively, scoring 34 goals, which was the second-highest total in the NHL, and his 39 points ranked him 3rd in the entire league. Denneny had a six-goal game against the Hamilton Tigers on March 7. Frank Nighbor had another great season with 18 goals, and Buck Boucher provided the team toughness, leading the club with 43 penalty minutes. Clint Benedict also had a great season, earning 14 wins and a league best GAA of 3.08. The team started the season 8–2–0 and won the first half of the season and a spot in the O'Brien Cup finals, but the Senators slumped to a 6–8–0 record in the second half leading to a playoff with the Toronto St. Patricks in a two-game total-goals series. On December 30, 1920, the Senators were ordered to give up Sprague Cleghorn to Toronto, on the orders of the league. The league ruled that the Senators were over the total salary limit for players and Cleghorn was ordered to report to Toronto. The same day, the league ruled that Punch Broadbent would have to go to Hamilton to complete a trade made before the season, still completed. Both players refused to report to their new teams. Cleghorn eventually reported to Toronto, but returned to Ottawa in time to play in the playoffs. Broadbent resumed play for Ottawa in the second half of the season.

December

The Senators finished December with a perfect 3-0-0 record, earning six points. They were in first place in the NHL, two points ahead of second place Hamilton.

January

At the end of January, the Senators had a 1-1-0 record in the second half of the season, earning two points. The Senators were in a tie for second place with the St. Patricks, two points behind the first place Canadiens.

February

Ottawa struggled to a record of 3-6-0 in February. Overall, the Senators second half record at this time was 4-7-0, earning eight points and third place in the NHL.

March

Ottawa finished the second half of the season with a disappointing record of 6-8-0, earning 12 and ranking third in the NHL, eight points behind the first place Toronto St. Patricks.

Final standings

Record vs. opponents

Schedule and results

Playoffs

Ottawa Senators 7, Toronto St. Patricks 0

In the NHL Championship, the Senators faced the Toronto St. Patricks in a two-game total-goal series with one game in each city. The series opened on March 10 in Ottawa. The teams skated to a scoreless first period. In the second period, Ottawa opened the scoring on a powerplay goal by Cy Denneny 1:45 into the period, giving the Senators a 1-0 lead. The Sens added a second goal less than five minutes later, as Georges Boucher scored to make it 2-0 Ottawa after two periods. The Senators continued to dominate in the third period, as they scored three goals, including two by Boucher, giving him three goals in the game, as the Senators shutout the St. Patricks 5-0 to take the series lead. The series resume four nights later in Toronto on March 14. The Senators played tight defense, and the game remained goalless after two periods. In the third period, Ottawa's Eddie Gerard scored the opening goal of the game, giving the Senators 1-0 lead. Four minutes later, Frank Nighbor scored, giving the team a 2-0 lead. Ottawa would win the series by a score of 7-0, advancing to the 1921 Stanley Cup Finals.

Ottawa Senators 3, Vancouver Millionaires 2

The series would take place in Vancouver, British Columbia at Denman Arena, and a record breaking crowd of 11,000 people would see the Millionaires win the first game 2–1 to take an early series lead. The Senators would rebound, winning the next two before Vancouver would tie the series up at two with a win in game four. Then, for the second straight year, the Senators would win the fifth and deciding game, winning the 1921 Stanley Cup, and became the first team since the 1912 and 1913 Quebec Bulldogs to win back-to-back Stanley Cup Championships. All of the contests in the series, which went to the full five games, were decided by only one goal. The Millionaires won games one and four with victories of 2–1 and 3–2, respectively. The Senators were victorious in games two and three with 4–3 and 3–2 wins. Then in the fifth game, Jack Darragh scored both of Ottawa's goals in the 2–1 victory to clinch the Cup. Darragh led the Senators in scoring with five goals during the series, while goaltender Clint Benedict only allowed just 12 goals in the five games, earning a 2.40 goals-against average.

Player statistics

Scoring leaders

Goaltending

Awards and records

Transactions

The Senators were involved in the following transactions during the 1920–21 season.

Trades

Free agents