Noonan will arrive at the City Ground as a free agent once his contract at Tallaght Stadium expires, meaning Forest will only be required to pay training compensation to Rovers and his former club, St Patrick's Athletic.
According to the Daily Telegraph, the move became possible once Noonan turned 18 in July, opening up the pathway to a British club under post-Brexit transfer rules.
The Kildare native rose to prominence in February last year when he scored on his senior debut for Shamrock Rovers, netting away to Molde in a Europa Conference League play-off. At 16 years and 197 days old, he became the competition's youngest ever goalscorer.
Bundesliga side Hoffenheim had appeared to be leading the race for Noonan's signature earlier this year, with Rovers accepting an offer in the region of €1.8 million for the striker, only for the player himself to opt against the move. Ajax also registered serious interest before his 18th birthday shifted the market firmly toward England.
Noonan progressed through Crumlin United and Ballyoulster before Pat's snapped him up in 2022. He initially found himself behind another highly rated forward, Mason Melia, in the pecking order at Richmond Park, prompting his switch to League of Ireland rivals Shamrock Rovers in January 2025.
Since making the move, Noonan has scored 17 goals for the Hoops, including eight this season, and has continued to catch the eye at international level. He starred as Ireland reached the last 16 of the Under-17 World Cup, scoring three goals in the tournament, and has since progressed to the Under-21 setup, netting once in six caps in a win over Andorra.
His most recent goal for Rovers came in a 3-3 draw away to Derry City, part of a run in which he found the net in three consecutive appearances. Manager Stephen Bradley will be able to call on him for the remainder of the campaign, with Rovers six games from a sixth Premier Division title in seven seasons and currently three points clear of St Patrick's Athletic and Bohemians.
Rovers have already exited the FAI Cup and Europe this season, leaving the league title as their sole remaining focus before Noonan makes his move to English football's top flight in the new year. Forest are understood to have fought off competition from Ajax and Benfica to secure his signature ahead of the January window opening.