[2] His first song for the group was "Gloria Swansong", and he continued to write by himself ("Pull Down the Blind", "Cable Car" 1971), with Allan Clarke ("Why Didn't You Believe", "Man Without a Heart", "Perfect Lady Housewife") and as part of Clarke-Hicks-Sylvester.

Some of Sylvester's work appeared on B-sides on singles including "Indian Girl" (1972),[5] "No More Riders" (1974),[6] in addition to singing lead vocals on the Tony Hicks and Kenny Lynch co-written song, "Oh Granny" (1972).

Sylvester sang "Long Cool Woman in a Black Dress" on the Hollies' 1973 US tour and on American television appearances.

On Out on the Road (1973), Sylvester took lead vocals on several songs including "Slow Down, Go Down", "Pick Up the Pieces", and "Mr. Heartbreaker" (which was co-written with Dean Ford of Marmalade).

After a period of discontent, partly over musical policy, Sylvester split with the Hollies in May 1981, in an incident that precipitated the resignation of bassist Bernie Calvert.

[14] In 2010, as a member of the Hollies, Sylvester was inducted into the Rock and Roll Hall of Fame along with Graham Nash, Allan Clarke, Tony Hicks, Bobby Elliott, Bernie Calvert and Eric Haydock.