Mason Jeffery-Off (b. 2004) is a Canadian double bassist, electric bassist and composer based in Montréal. Originally from Ottawa, Jeffery-Off graduated with a Bachelor’s Degree in Jazz Performance at McGill University in 2026. There, he studied with Ira Coleman and John Hollenbeck. He performs regularly with Jean-Michel Pilc, Darrell Green, and Kevin Dean, and has also appeared with the National Arts Centre Orchestra.

At 18, Jeffery-Off was one of 16 international jazz musicians under the age of 25 to be selected for Betty Carter’s Jazz Ahead, a performer-composer residency located at the John F. Kennedy Center for the Arts in Washington DC. In 2024, he received the Hnatyshyn Developing Artist Grant (Oscar Peterson Grant for Jazz Performance).

Jeffery-Off leads Marvelous Creatures, an ensemble performing compositions that transform the melodic contours of spoken and written language into music. He also leads a trio with Ben Shaw on drums and Sam Fortin on piano performing his original music across Montréal. Jeffery-Off’s work bridges jazz, 20th-century classical music and folk.

Jeffery-Off’s EP ‘Everything Shifts’, is set for release in late July of 2026.