Son of an Irish father and French mother, Hart grew up playing amateur rugby in Dublin for Clontarf FC and also spent some time with grandparents in Toulouse, an area with a strong rugby culture.

[1] In 2011, he accepted a trial invitation from French Rugby Pro D2 side Grenoble, where ex-Leinster player Bernard Jackman was a coach, and earned a place in the club's academy.

[3] On 24 January 2017, it was announced that Hart would be joining Irish province Munster on a two-year contract, beginning at the conclusion of the 2016–17 season.

[4] Hart made his competitive debut for Munster on 1 September 2017, coming off the bench against Benetton in Round 1 of the 2017–18 Pro14.

[5] He made his first start for Munster on 26 November 2017, doing so against Zebre and scoring his first try for the province in their 36–19 away victory.