The 23-year-old passed his medical in Dortmund and has signed a five-year contract, with the two clubs settling on a deal reported at €26 million guaranteed plus up to €6 million in bonuses — a package that could reach €32 million in total — and PAOK also securing a sell-on clause worth 15%.
According to Greek media, two Dortmund youngsters could yet become part of the wider transfer picture as a separate matter.
Sport24.gr reports that PAOK are in advanced discussions over Christos Kostoglou, a 17-year-old central midfielder who plays for Dortmund's Under-19 side and has a year remaining on his contract. Dortmund are said to be willing to let him leave on a free transfer.
Talks over 18-year-old Samuele Inácio are not as advanced. According to Gazzetta, Saloniki are interested in taking the Italy youth international on loan, though he is considered a genuine part of Borussia Dortmund's first-team plans at Strobelallee.
A door could still open in the closing days of the window, but only if the prospect of regular minutes at Dortmund diminishes given the volume of new arrivals at the club this summer.
Konstantelias, capable of playing across the offensive midfield and left-wing positions, becomes Dortmund's answer to missing out on Said El Mala earlier in the window, with sporting director Nils-Ole Book having identified pace and one-on-one dribbling ability as priorities following Karim Adeyemi's departure to Barcelona. In his time at PAOK, Konstantelias made 190 appearances, scoring 44 goals and providing 26 assists, while also winning 18 caps for Greece.
The move has not gone down well with sections of PAOK's own support, with reports of protests outside the club's offices from the "Gate 4" ultras group, who consider Konstantelias — a product of the club's own academy — a symbol of the club rather than a player to be readily sold.
That backlash did little to slow the deal itself, with Konstantelias having already flown to Dortmund and completed the formalities before the protests intensified.
At Signal Iduna Park, Konstantelias will link up with fellow Greece international Konstantinos Karetsas, who is said to have given his new teammate a positive account of life in the Ruhr before the move was finalised.