JAKARTA, Indonesia—The candidate determined to have lost Indonesia's presidential election last month waged a last-ditch effort in court on Wednesday to have the results overturned, while his camp said that even should he fail he'll push his agenda in the legislature his allies currently control.

Prabowo Subianto, a former army general, said that "systematic and massive cheating" cost him the tightly contested two-man race. The country's election commission declared July 22 that had he lost by 8.4 million votes...