Borowy debuted on April 18, 1942 with the Yankees, finishing with a 15-4 record, 85 SO, 2.82 ERA. Then, he started Game 4 of the World Series against the St. Louis Cardinals without a decision.

In 1943 Borowy went 14-9, 107, 2.82, and won Game 3 of the World Series against St. Louis. Named an All-Star in 1944, he pitched three scoreless innings in the game, ending the season with 17-12, 107, 2.64.

Borowy enjoyed his best season in 1945 when he pitched for both the Yankees and Cubs and registered a combined 21-7, 82, 2.65, between the two teams. After a 10-5 start with the Yankees and being selected again to the All-Star Game, he was put on waivers inexplicably and was passed over by 15 teams. The Cubs snatched him for $97,500. Borowy went 11-2 for the remainder of the season, including three wins over the Cardinals down the stretch, and led the National League in winning percentage (.846) and ERA (2.14), as the Cubs won the pennant behind a Borowy's 4-3 win over Pittsburgh. The final margin for Chicago was 3 games over the Cardinals.

On October 3, 1945, the Tigers and Cubs meet in the World Series for the 4th time. In the opener, Borowy pitched a 6-hitter 9-0 shutout. He lost the fifth game, and then came back to win the sixth with four scoreless relief innings. Borowy started the final game on one day's rest but gave up hits to the first three batters before leaving. He took the loss and the Tigers won the Series. Borowy helped put the Cubs into their last World Series, and led to the end of Joe McCarthy's 15-season tenure as Yankees manager. Throwing away a potential pennant and selling the staff ace in the midst of the race was something he couldn't understand. Then, McCarthy resigned in 1946.

In the remainder of his career, Borowy was plagued by finger blisters and a chronic sore shoulder. He pitched his final game on September 14, 1951.

Hank Borowy died in Brick Township, New Jersey, at age of 88.