The 19-year-old has joined the likes of Jadon Sancho, Jude Bellingham, and Jamie Gittens on the list of English youngsters to make the move to Dortmund with his options limited under Mikel Arteta.
However, Nwaneri will be hoping he can still prove himself with the Premier League champions, if he can get back on track during his time in Germany.
The teenager looked set to be a first-team regular for Arsenal after bursting onto the scene, and he retains the record as the youngest player in Premier League history, following a club debut aged just 15 years and 181 days old against Brentford back in 2022.
As per reports from Sky Sports Germany, the deal does include the option to recall Nwaneri in January, if Arteta is struggling with squad injuries or the Spaniard decides his form deserves a shot at Arsenal in the season half of the campaign.
Nwaneri could make his Dortmund debut tomorrow in a Bundesliga clash away at Hoffenheim.