The England Under-21 international, 20, has joined the club until the end of the season, the Championship side has confirmed.
In-demand Balogun has made 16 appearances in total for the London club and scored twice in five Europa League appearances last time around.
Boro boss Chris Wilder has described him as a ‘natural finisher’ and is delighted to sign him on loan, having beaten off competition from elsewhere for his loan signature.
Balogun has scored 13 goals in 11 PL2 starts and two goals in the Papa John’s Trophy so far this campaign and Wilder says he has been following his career for some time.
Wilder said: “We’re delighted to get Flo in.
"He’s a player I’ve known about for a long time and we identified him as someone who could come in and improve us in the second half of the season.
“He has great movement, good pace, and he’s a natural finisher. We’re looking forward to working with him.”
He is the third January signing, following in Aaron Connolly and Caolan Boyd-Munce.
Meanwhile, young defender Will Kokolo has joined League One side Burton Albion.
The 21-year-old, who made his first team debut at Luton in November and his first senior start at Mansfield Town in the FA Cup last weekend, joins Albion on a permanent basis.
The former Sunderland youth came through the youth ranks at Monaco before his switch to the Stadium of Light in 2017.