The 16-year-old has revealed that he penned a pre-contract agreement with the Red Devils in January and will finalise a one-year scholarship deal this weekend.
Galbraith, who is the captain of Northern Ireland's Under-17s, was invited to have trials with the Premier League giants last year.
"I went on a couple of trials last year after I was spotted playing for Linfield U16s. I must have done okay because United then offered me a contract in January," Galbraith told the Irish Mirror.
"The trials were good, and I was playing with top players as well. Players like Angel Gomes who is moving onto the first team now. I played in a couple of friendly games and also some training sessions and it was a great experience.
"I signed the pre-contract in January and I will finally travel over to Manchester this weekend to live there and sign my full deal. It is one-year scholarship and then two-year pro deal. I will be playing with the Under 18s next season, but the big aim is to progress to the first team."
Galbraith has the option of a two-year professional contract.