Guptill attended Avondale College and played in the school's 1st XI cricket team. He was also a prefect in his final year.
At the age 13, Guptill was involved in a forklift accident and lost three toes. (This fact was revealed to the world by provincial teammate Scott Styris whilst Styris was commentating on Guptill's ODI debut. This has since earned Guptill the nickname "Two Toes" within the Black Caps team).
He made his One Day International debut for New Zealand on 10 January 2009 against the West Indies in Auckland, becoming the first New Zealander to score a century on his one-day debut. He reached the landmark with a huge six off the bowling of Chris Gayle. His score of 122 not out is the highest debut score in New Zealand ODI history, and second highest debut score ever in ODIs. He also gained the highest ODI score for a New Zealander against the West Indies and became the first cricketer from his country to carry his bat through a completed innings. He made his Test debut against India in the first Test in Hamilton in March 2009, scoring 14 and 48.
On 14 December 2009, Guptill made his test bowling debut in the second innings of the match against Pakistan in Napier. In his innings, he made two 'caught and bowled' deliveries to Salman Butt and Imran Farhat. At that point, he had 2 wickets for 16 runs. The test ended in a dour draw due to rain, but he ended with 3 for 37 in 13.2 overs, when he trapped Mohammad Asif for lbw after referral for the final wicket of the Pakistani innings.He is one of three players to score 30 runs or more in 5 consecutive t20 innings.
In the 2013 tour of England, Guptill led from his opening position scoring back-to-back undefeated hundreds. At the first ODI at Lord's Cricket Ground, he guided a successful chase scoring 103* with a strike-rate of 83.73, following up with a 189* (strike-rate of 121.93) at the Rosebowl, Southampton in the second game. His 189* was, at the time, was the highest score by a New Zealander in an ODI, and contributed to the fifth-highest team total in ODI history (359). With the innings, he also equalled the record set by Viv Richards for most runs scored in an ODI on English soil.
Guptill surpassed his best of 189, in the 2015 World Cup, scoring an unbeaten 237 off 163 balls, against West Indies, in the quarter-finals on 21 March, at the Westpac Stadium in Wellington, New Zealand. His innings included 11 sixes and 24 fours and the team finished at 6/393, the best total in a World Cup knockout match. It was a remarkable turnaround in form for him, given he went from three ducks in the lead-up matches, to scoring two fifties, a century and the 237 in the quarter finals. Ending the tournament with 547 runs, he emerged as its highest scorer, with his team finishing second to Australia.
Guptill scored back to back unbeaten ODI centuries against England during Tour of England in 2013. He scored 330 runs in the 3 match ODI series which eventually was a world record for scoring most runs in a particular 3-match bilateral ODI series, which was later surpassed by Tillakaratne Dilshan. He was also named the man of series
He is the first New Zealander and the 5th overall in the world to score a double century in an ODI. His 237* score currently holds the record of highest individual score in World Cup cricket and the second highest score in One Day Internationals.
He is the first man to face the pink ball in a day-night Test match. He faced the first ball of the first ever day-night match against Australia in Adelaide for Aussie pacer Mitchell Starc. In the match, Guptill also became the first man to be dismissed in a day-night match, when he got lbw for Josh Hazlewood.