The 19-year-old Republic of Ireland youth international becomes the second forward to head to Rodney Parade on deadline day, following Manchester United’s Charlie McNeill through the door.
Kavanagh, son of former Cardiff City great Graham, spend the second half of last season on loan at Harrogate Town.
The forward has been prolific at age-grade level for Middlesbrough and, like McNeill, will now aim to take that goal-scoring form into League Two.
“I’m delighted to get the move over the line, I’ve been wanting to get a loan this window and this managed to come around so I’m really happy,” said Kavanagh, who was born in Cardiff while his father was playing for the Bluebirds.
After scoring six goals in 13 games in the Under-18 Premier League, the striker signed professional terms at the Riverside in 2020.
His first professional season at Boro led to a successful season of 13 goals in 20 Under-18 Premier League matches as well as two in three in Premier League Two and three in three in the FA Youth Cup.
Last season, Kavanagh netted six times in as many games in Premier League 2 as well as five in four in the Under-18 Premier League, which earned him a January move to Harrogate Town where he scored once in 12 games.
His fine goalscoring carried on into this campaign with a further seven goals from 11 matches in PL2 while he scored once in four appearances for Republic of Ireland Under-17s.