A Linwood Keas player, a Canterbury representative Greengrass made his debut for the New Zealand national rugby league team in 1970 at the World Cup.

He was also part of New Zealand's squad at the 1970 and 1975 World Cups and toured Great Britain and France in 1971 and Australia in 1972.

[3] His international career was ended in a World Cup match against Wales.

[3] Greengrass became engaged to Christine Joy Ellis in February 1972,[5] and the couple married in Ashburton later that year.

From 1974 to 1984 she was involved with the local Plunket Society, serving in roles including chair, secretary and treasurer.