It will bring to an end Hackney's long association with his hometown club, and while the deal isn't quite complete at this stage, it's expected to be finalised in the coming days.
At least half a dozen Premier League clubs were interested in Hackney this summer, but a move to Everton has always been the preference for the Teessider.
The Toffees had their opening approaches for the 24-year-old turned down, but negotiations have continued and the Premier League club are now closing in on one of their top summer targets.
RECOMMENDED READING:
Nottingham Forest, Crystal Palace, Fulham and Hull City are among the other clubs who have been monitoring Hackney's situation, while Boro's former boss Michael Carrick remains an admirer, but a move to Manchester United always felt unlikely this summer. Hackney was identified as a top target by David Moyes, and Everton failed with two bids before significantly increasing their offer.
Boro made it clear to interested clubs at the start of the summer that they won't budge on their valuation of Hackney, and they've been true to their word.
Hackney had entered the final year of his contract at the Riverside but Boro were willing to keep the midfielder if their asking price wasn't met.
Hackney's exit was always extremely likely, however, and Boro have ensured they are prepared for their star's departure, with several potential midfield targets lined up.
Oliver Skipp is one of the players who has been in the club's thinking but Boro will move on to other targets because of Leicester's demands. The Foxes reportedly want £15m for the former Tottenham man.
Boro have several midfield targets lined up and will make more than one signing in that department this summer.
As reported by the Northern Echo last week, a return for Alan Browne after his loan spell from Sunderland last season is extremely unlikely.
Hackney will leave Boro having made more than 150 appearances for his boyhood club. He broke into the first team fold after Chris Wilder's exit as head coach and established himself as one of the brightest talents in the EFL under Michael Carrick.
Hackney is coming off the best season of his career, though the midfielder missed the promotion run-in because of an ankle injury sustained in the March draw with Bristol City. He returned from the bench for the final quarter of the play-off final against Hull City but couldn't prevent the Tigers snatching promotion through Oli McBurnie's stoppage time strike.
Boro are now preparing to try and go one better next season and Kyle Joseph is set to become the club's first signing of the summer.
Boro are closing in on the capture of the 24-year-old Hull City attacker in a £5m deal.
The Tigers need to raise around £6m before close of play on Tuesday to ensure they don't fall foul of Premier League financial regulations, which would potentially result in a points deduction.