On March 27, 2017, Lettieri signed a two-year entry-level contract as a free agent with the New York Rangers of the National Hockey League (NHL).

[2] He was invited to the Rangers training camp before the 2017–18 season but was cut and sent to the Hartford Wolf Pack before the final roster was made.

[6] After four seasons within the Rangers organization, Lettieri left as a free agent and signed a one-year, two-way contract with the Anaheim Ducks on October 10, 2020.

[12] Towards the end of the 2022-23 season, with the Bruins comfortable in the standings, Lettieri was once again called up in order to rest key players.

[13] As a free agent from the Bruins, Lettieri returned to his home state in agreeing to a two-year, two-way contract with the Minnesota Wild on July 1, 2023.

[15] Lettieri's grandfather, Lou Nanne, played, coached and was the general manager of the Minnesota North Stars.