Soren, 62, was present in the court when the judge pronounced the verdict and was immediately taken into custody and sent to Tihar jail after a medical check-up at AIIMS. The length of sentence will be announced next Thursday.
Additional Sessions Judge B R Kedia found Soren guilty of kidnapping and hatching the conspiracy to kill his secretary. However, the court acquitted two other accused, Sunil Khaware and Asish Thakur.
Earlier, in his tenure in government, Soren had to resign after a Jharkhand court issued a non-bailable warrant against him in connection with a murder case during a protest agitation in the early 1980s.
The Court said Soren was guilty under sections 120-B (criminal conspiracy) read with 364 (kidnapping or abducting in order to murder) and 302 (murder) of the IPC.