The 21-year-old England Under-20 international has signed a five-year contract after attracting interest from several clubs.
Lankshear arrives with valuable Championship experience, having scored 11 goals in 43 appearances for Oxford United last season while winning the club’s Young Player of the Year award.
“Middlesbrough is such a massive club over the years; I deem it to be a Premier League club,” Lankshear told club media.
"The project here really excites me. I can’t wait to get started and be part of the journey, and get this club back where it belongs."
The forward previously spent time on loan at West Brom before making his Tottenham debut in both the Europa League and Premier League during the 2024/25 campaign.
Lankshear becomes Boro’s fourth summer signing, following Jeremy Sarmiento, Myles Peart-Harris and Kyle Joseph, as the club targets promotion back to the Premier League.