After two seasons in the Greek Super League, the former Arsenal man moved to the Riverside Stadium outfit for an undisclosed fee after successful medicals.
Thus, he becomes Neil Warnock’s fourth summer signing after Sam Morsy, Marcus Bettinelli, and Grant Hall. There, he will link up with former teammate Britt Assombalonga.
According to the former England international of Nigerian descent, the dream of playing in the Premier League fuelled his decision as well as the role played by manager Warnock.
"It's an amazing feeling to sign, everyone knows the history of the Boro," Akpom told their club website.
"Hopefully we can push for promotion, I know that's the aim of the team and hopefully I can help with that.
"When a team like Middlesbrough comes in you don't need much convincing, it's a top club."
He also claimed his experience in Greece would come handy for him and thinks he can add to the depth of quality in Boro’s frontline.
"I felt like I needed it. It was like a refresh for me, different style of football, different culture, different everything really," he continued.
"To come back here, I'm more motivated and I'm sure it will go well.
"I know the league, I was here with Hull and Brighton when they got promoted, so hopefully I can boost the team.”
He added: "The manager sounded very convincing - he's got a plan, and all the players need to do is work hard and follow his vision.
"I'm ready to meet him and I'm ready to work.
"It's a good team, we've got some good strikers. We can all push each other - that's how it should be. There's a lot of games in the Championship, so there's not always a starting XI. I'm ready to join them, I can't wait."
For the 2020-21 campaign, Akpom will wear jersey no. 10 worn by English youngster Marcus Browne last term.
He could make his debut when Middlesbrough travel to Loftus Road on Saturday for a date with Bright Osayi-Samuel’s Queens Park Rangers.