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 .