Howarth attended Auckland Grammar School, where he was a pace bowler. After he left school he had back trouble, and his coach, Merv Wallace, suggested he take up spin bowling. He became an orthodox left-arm bowler, and made his first-class debut in 1962.

Between the years 1969 and 1977, Howarth played 30 tests for New Zealand, capturing a total 86 wickets at an average of 36.95. Justin Vaughan chief executive of New Zealand Cricket credited Howarth with playing a significant role in New Zealand's international cricket history, crediting Howarth's "five-wicket bag against India at Nagpur in 1969 was a match winner that helped give New Zealand its first ever test win on the sub-continent". India were chasing 277 in the fourth innings but it was Howarth's 5 for 34 that gave New Zealand the lead, highlighted by a catch off his own bowling, ending a 167-run win. Howarths's other five-wicket haul was in a Test against the Pakistan national cricket team in Karachi, when he picked up 5 for 80 .

Howarth was a part of the New Zealand national cricket team that played in the 1975 Cricket World Cup in England, making it to the tournament semi-finals.

March 1977 marked his retirement from Test cricket. After retiring, Howarth devoted his time to his family's fishing business, Kia Ora Fisheries, later Kia Ora Seafoods.^[5][6]

Howarth died at age 64 on 7 November 2008. A cause of death was not initially disclosed,^[4] though Howarth had been battling cancer for some time.^[5]

Test 5 Wicket hauls