The 19-year-old centre-half came through the ranks with Spurs and has been a regular feature in their Under-18s side over the course of recent seasons.
He also played twice in Premier League 2 for Tottenham’s Under-21s last season. But the teenager was released last month, which allowed Boro to make their move.
Baptiste will initially link up with Boro’s Under-21s.
Baptiste is the second youngster to join the club this week, with Boro having signed teenage goalkeeper Owen Foster from Hull City. That deal followed a successful trial for Foster at the end of last season.
Where Baptiste is concerned, Boro have had success signing young players from the capital in recent years.
Djed Spence moved to the Riverside as a youngster after his Fulham release, before going on to join Spurs in a big-money move, while Isaiah Jones was spotted in London’s non-league scene and made more than 130 league appearances. He left for Luton in a £5m deal in January.
Martin Carter, Boro’s head of academy recruitment, previously told The Athletic: “London is a hotbed of young players
“There’s such a population in London that the super-clubs can rule boys out. We’re trying to rule them in.
“They’re going for boys at this level — high — and we’re going for those at this level — medium. Realistically, we aren’t getting the highest level but we’re looking for a boy who can get to that level. That’s what scouting is.”
