The 21-year-old Academy graduate was a regular for the Under 23s side in recent seasons, making 41 appearances in Premier League 2 matches and scoring 11 goals.
The attacking midfielder joined West ham at the age of eight. A skilful player capable of playing across the forward line, Browne made his senior debut and only appearance for West Ham as a substitute in the UEFA Europa League Play-Off round draw at Romanian side Astra Giurgiu in August 2016. Browne has also spent time on loan at Wigan Athletic and Oxford United.
Last summer he travelled with the first-team squad for pre-season training and appeared in the 3-2 defeat by FC Winterthur in Austria on 8 July 2018.
“I felt at this stage and at this time, and after speaking to the gaffer and some of the players here, that this is the perfect move for me,” Browne told the Boro club website.
“I like to be direct, run at people, I like to be creative and attack. feel like the style of play and philosophy the gaffer has here will suit me really well.”