He has performed with musicians such as Charles Lloyd, Wayne Shorter, Pharoah Sanders, McCoy Tyner, Chick Corea, John Handy and Sun Ra.
[2] The New Grove Dictionary of Jazz states that "Some critics regard Greenwich as the most important Canadian jazzman".
He is listed as one of the '10 Best Canadian Jazz Musicians of All Time' in the Canadian Book of Lists, and in The History of the guitar in jazz Barney Kessel writes, "There is a deep emotion and sincerity in Sonny's music ... and I consider him a really rare kind of talent".
In 1968, S[3]onny Greenwich led his own quartet, of pianist Teddy Saunders, bassist Jimmy Garrison and drummer Jack DeJohnette at the Village Vanguard in New York.
In December 1969 Greenwich performed with Miles Davis, Wayne Shorter, Chick Corea, Dave Holland and Tony Williams at the Colonial Tavern in Toronto.