[2][3] Barrett played at under-20 and Sevens levels for New Zealand before being called into the All Blacks squad in May 2012, and made his international debut as a replacement in the final test against Ireland in Hamilton, when he kicked nine points, on 23 June 2012.

He has four brothers and three sisters, including Kane, a former Blues representative and Taranaki captain and current All Blacks, Scott and Jordie.

He attended St Fiach's National School in Ballinacree, where he and his brother Kane learned how to play Gaelic football.

[8] The 19-year-old had made a huge impression in his opening season for the province, especially in his ability to attack the line and create space which saw him named most promising player of the year.

He made his debut in a 50–47 win over the Cheetahs in Bloemfontein, a match that saw the Hurricanes prevail on full-time with a try to lock Jeremy Thrush that Barrett converted.

[12] With Barrett playing, Taranaki finished a respectable third placing in the ITM Cup and was instrumental in securing his side the Ranfurly Shield off Southland.

Barrett lead effectively with two try assists, one for second five Tim Bateman and another for reserve hooker Motu Matu'u that was later disallowed by the television match official.

He landed all nine of his conversion attempts, eclipsing the previous mark of six shared by Christian Cullen, Willie Ripia and Jimmy Gopperth.

[16] Barrett's Test debut was a memorable one; the first five-eighth coming off the bench after 24 minutes and helping the All Blacks contribute 9 points to a record 60–0 win over the Irish.

[17] Barrett was then released from New Zealand national coach Steve Hansen to start in his first run-on against Wellington since Taranaki's successful Ranfurly Shield defence against Tasman on 1 September.

[26] Along with Julian Savea, he started all sixteen matches for the Hurricanes and by early April, in the 2014 Super Rugby season, Barrett had already scored 100 points.

[citation needed] Despite having a tough night with his goal-kicking, succeeding with only one from five attempts, he produced a strong 55-minute performance and were involved in setting up the team's three tries.

On 18 October 2014, despite Cruden returning to the team squad for the third Bledisloe Cup match in Brisbane, coach Steve Hansen selected Barrett to start at No.

Barrett was selected for the 2015 Rugby World Cup, starting in one fixture against Namibia, and coming off the bench to cover wing and fullback in the rest.

Barrett returned to Taranaki in 2015, after missing the 2013 and 2014 seasons for the province after featuring at first five-eighth against Otago in round three of the competition.

With three minutes left in the first half, he sized up his options perfectly again to slip a kick across field where right wing Codey Rei was waiting in clear space to secure the ball and score.

He was named man of the match in the Super Rugby final, scoring 15 points as the Hurricanes beat the Lions 20-3 to win their first title.

Due to his superb form for the Hurricanes and against Wales during their tour; Barrett supplanted an injury-plagued Aaron Cruden at fly-half for the 2016 Rugby Championship.

Barrett scored 24 points including two tries in his 50th test match, against Samoa, on 16 June 2017, which was also his brother Jordie's debut.

In the final match of the Rugby Championship against South Africa, Barrett was subbed off after only 33 minutes for a concussion test, being replaced by Lima Sopoaga.

Barrett scored the first All Black try of 2018, but he had limited participation in the three-test 2018 Steinlager series against France, due to injury.

Barrett was taken off the field for a concussion test, which he failed, due to a mid-air clash with French fullback Benjamin Fall.

Barrett performed well in the last round of the competition, when he was moved to fullback, after Richie Mo'unga replaced winger Waisake Naholo.

Barrett, Mo'unga and Hurricanes loose forward, Ardie Savea, had a commanding teamwork in the last 20 minutes, allowing the All Blacks to beat South Africa 32-30.

Barrett's 2018 end-of-year tour saw him surpass Dan Carter as the most prolific try-scorer to ever play at first-five,[citation needed] as he scored the 31st of his career in the third Bledisloe Cup test, against the Wallabies, off a pass from Rieko Ioane, during a 37-20 win.

With Richie Mo'unga on the bench, and Damian McKenzie at fullback, Barrett was one of three first-fives fielded by New Zealand on the day.

Barrett's performance against England also saw him kick the first drop-goal of his professional career, in the 46th minute, answering the ongoing criticism for his goal-kicking.

Underhill's try was ruled out due to an offside charge down from replacement forward, Courtney Lawes, which left Barrett's 100% kicking percentage as the way New Zealand won the test.

[43] Barrett returned for the international season and on 30 October 2021 he played his 100th test match, in the fixture against Wales at Principality Stadium in Cardiff.

Barrett proposed to his long-time partner Hannah Laity in 2018 and they married the following year in a private ceremony on Rakino Island.