On October 15, Dellandrea scored his first career OHL multi-goal game, as he had two goals and an assist in a 5–3 loss to the Barrie Colts.

Six days later, Dellandrea earned his first career OHL playoff point, assisting on a goal scored by Kole Sherwood in a 5–2 loss to the Sault Ste.

Dellandrea recorded his first career OHL hat-trick on December 16, as he scored three goals, as well as added two assists for a five-point game, in a 5–2 win over the Sarnia Sting.

[3] On November 20, Dellandrea recorded the second hat-trick of his OHL career, as he scored three goals in a 6–4 loss to the Sarnia Sting.

Just over two weeks later, on December 5, Dellandrea recorded another hat-trick, as he scored three goals, as well as an assist, in a 5–2 win over the Barrie Colts.

The following day, on March 20, Dellandrea appeared in his first professional hockey game, in a 6–3 victory over the Grand Rapids Griffins.

Called up to the NHL for only one game in the regular season in 2021–22 and one game in the postseason 2022 Stanley Cup playoffs, Dellandrea made the opening night roster for the 2022–23 NHL season, playing on the second line alongside Tyler Seguin and Mason Marchment.

[7] After seven years with the Stars organization, Dellandrea was traded to the San Jose Sharks on June 19, 2024, in exchange for a 4th-round pick in 2025.