Born in Palmerston North and educated at Palmerston North Boys' High School, David O'Sullivan began playing as a left-arm spin bowler for his local team Manawatu in the Hawke Cup in 1966–67.
In 1971 he took 50 wickets at an average of 14.80, and was "the backbone of the county's second eleven championship success", the team going through the season unbeaten.
He was overlooked for the 1973 tour of England in favour of Eric Gillott, and returned to Hampshire.
[4] Hampshire wanted to retain him for 1974 but decided to choose Andy Roberts as their second overseas player instead.
Howarth was unavailable for the tour of Australia in 1973–74, and O'Sullivan took his spot in the Test team as senior spinner.
[10] O'Sullivan continued to play successfully in New Zealand domestic cricket until the 1984–85 season when at the age of 40 he bowled more than 400 overs and took 38 wickets at 27.60.