Robertson left Hawke’s Bay to go to teachers’ college at Ardmore, immediately gaining the attention of Counties selectors in a development grades team in 1970.
He made his debut at first-class level at second five-eighths for Counties in 1971, and three months later played at centre for the North Island in the annual inter-island match, despite not having played in the trials.
The New Zealand Rugby Almanack named him one of the five most promising players in New Zealand and he made his debut for the All Blacks against the touring Wallabies in August 1972, aged just 20.
Including the 1976 tour of South Africa and the Grand Slam tour of the UK two years later, when the All Blacks had a clean sweep of wins over the home nations, England, Ireland, Scotland and Wales for the first time, he played 34 test matches.
He retired from international rugby after a home test against Scotland in 1981, when he made himself unavailable for the ensuing tests in the tumultuous Springboks tour, retiring from inter-provincial rugby the following season after playing 135 matches for Counties (now Counties Manukau).
He was back in Hawke’s Bay in 2017 as one of the first inductees on Hastings Boys’ High School’s Wall of Fame, along with Hillary Everest mission member George Lowe (posthumously), and businessmen Sir Selwyn Cushing and Craig Hickson.