Mr Leeson, who was detained at Frankfurt airport in March, has been held in formal detention since early May after a Frankfurt court approved one of 12 allegations in Singapore's extradition request.
The Frankfurt regional high court has now said that the other 11 charges also met initial criteria for extradition. Singapore may only try Mr Leeson on charges approved by the German court in the extradition request.
He will appear before a local judge next week to be informed of the court decision and also to present his defence seeking to block extradition.
The 28-year-old Briton, who faces up to seven years in prison on each of the 12 charges of forgery and cheating, has been hoping to be sent to Britain to stand trial. But British authorities have not sought to have him returned to London.
He will remain in the Frankfurt jail where he has been held since his arrest on 2 March at Frankfurt airport pending a final court ruling on the legal validity of Singapore's request, expected in the next three to four weeks. Mr Leeson will probably remain in Germany pending an expected protracted legal battle over the extradition request until the autumn.Reuse content