Doug started playing rugby seriously at Auckland Grammar School where he was also a star sprinter (he once clocked 10.68s for the 100m), captain of athletics and head prefect.
He was selected for the New Zealand team at under 16 level, New Zealand Secondary Schools and New Zealand Colts where his high work rate, superior speed and fantastic defensive work put him well on his way to a successful rugby career.
He made his first class debut for Auckland at 18 and in 1997 scored 3 tries in his first Super 12 appearance where he was the youngest ever debutant at the time. He spent the majority of his Super Rugby career with the Blues where he scored 59 tries (still a Super Rugby record) in 108 appearances. Doug also jointly holds the record for the most tries (4) scored in a single match (vs Hurricanes 2002) and helped the Blues to win the 2003 championship.
Doug debuted for the All Blacks on 16 June 2000 against Tonga where he scored 2 tries (one after only 22 seconds of getting on the field) and continued to score an average of 4 points a game for his test career. Doug played in the 2003 and 2007 Rugby World Cups and his hat-trick against Italy on 8 September 2007 brought him level with Christian Cullen’s record for the most tries scored by an All Black. On 23 September Doug scored in the 15th minute against Scotland to make the record his own.
In 2006, together with fellow All Black Ali Williams, Doug became a founding patron of the KidsCan Charitable Trust, a New Zealand charity which provides clothing, shoes and food to children in low decile schools so they can attend school and reach their full potential in life.
Doug's interest in helping children reach their potential in sport, regardless of their financial circumstances caused him to launch the Doug Howlett Outreach Foundation in 2007 which helps children in low decile schools throughout New Zealand.
In 2008, Doug moved to Europe to play for Irish Club Munster where he currently plays in the Magners League and Heineken Cup competitions. He scored his first try against Ulster on 22 March 2008.
In May 2008 Munster beat Toulouse 16–13 to win the 2008 Heineken European Cup making Doug only the second player to have won major rugby tournaments in the Northern and Southern hemispheres.