The Ecuadorian international ended his loan with Italian Serie A side Cremonense and will now make the switch to the Championship, a move that he says he cannot wait to get started with.
“I’m very pleased to finally be here. The ambition from everyone at the club is what attracted me to Boro.
"I’m hungry to get going, and I can’t wait to show people what I can do.”
The 23-year-old former Charlton and Benfica winger made 21 appearances for Brighton, including six starts and scored his first goal for the club in last season’s 4-0 win over Crawley Town in the EFL Cup.
Sporting director Jason Ayto said: "This is a great opportunity for Jeremy and gives him the possibility of a permanent move if things go well, with a club challenging for promotion to the Premier League.
"He knows the Championship well having been part of two promotion-winning squads with Ipswich Town and Burnley.
"I haven't had the opportunity of working with him, but I know he has been a great professional and those a pleasure to work with.
“We wish him every success at Middlesbrough."
The youngster will be aiming to complete the promotion hat-trick with second-placed Boro after helping Ipswich and Burnley to the Premier League over the past few years.