Despite interest from Manchester United, a fee in the region of £26m has been agreed for the 17-year-old, which would make him the most expensive player of that age in the world.
On Thursday morning, Bellingham flew to Dortmund on a private jet, where he is expected to undertake his medical in the coming days.
The Englishman became Birmingham’s youngest player in history when he made his debut against Portsmouth in the League Cup, and has continued to develop into one of the most exciting young prospects in English and European football.
He has gone on to score four goals and assist two others for the Blues in the Championship so far this campaign, in a team which has struggled in the bottom half of the table.
At national level, he has captained both the England U15s and U17s.
In January, Bellingham was heavily linked with a move to Man United and was even invited for a tour of their Trafford Training Centre.
Dortmund have allegedly won the race to sign him due to their track record of bringing young players through to feature in the first team at a young age, while they can also point to the success of Jadon Sancho who joined from Manchester City to become one of the elite wingers in Europe thanks to the opportunities he has been awarded.