After coming through the youth setup at Hartlepool United, Kieran made his first-team debut for the Victoria Road club in October 2014 as a 17-year-old against Sheffield United in the Football League Trophy.

Following loan spells with Spennymoor Town and Frickley Town, the latter in 2015, he made a temporary switch to Gateshead in 2017. After impressing sufficiently, he made a permanent move to the Heed that summer.

That campaign, though, saw another loan move, this time to Blyth Spartans in the National League North. After being recalled from that move in January 2018, he joined them again the following month before signing permanently in June 2018.

After a campaign with the Croft Park club, and one where he established himself as a regular starter for the first time, he made the move to York City, also in the National League North.

The step up to full-time football with the Minstermen suited him and, after a strong first season, stepped up to the National League with FC Halifax Town. After fifty-five league appearances across two seasons, he joined the Mariners in July 2022, signing a two-year deal ahead of our return to the EFL.

In his first season in black and white, Green made thirty-one league appearances, as well as featuring regularly in our run to the Emirates FA Cup Quarter-Finals.