Former sub-postmaster and campaigner Alan Bates has said the Post Office spent 23 years trying to "discredit and silence" him.
In a strongly worded witness statement to the public inquiry into the Horizon IT scandal, he accused the Post Office of lying about the accounting system.
Mr Bates told the inquiry that "it was pretty obvious" the Post Office were "after me" after he repeatedly raised concerns about Horizon.
His contract was terminated in 2003.
Between 1999 and 2015, hundreds of sub-postmasters were wrongly prosecuted due to the faulty Horizon software, which showed errors that did not exist.
Alan Bates has been campaigning on behalf of sub-postmasters for decades, and was recently catapulted into the national spotlight by an ITV drama about the scandal, Mr Bates vs The Post Office.
In his witness statement he said: "Prior to and since my termination from the Branch, I have spent the last 23 years campaigning to expose the truth, and justice, not just for myself, but for the entiregroup of wrongly treated/wrongly convicted SPMs (sub-postmasters).
"I have dedicated this period of my life to this cause which, sadly, has been necessary since Post Office Limited ("POL") has spent this entire period denying, lying, defending, and attempting to discredit and silence me and the group of SPMs that the Justice For Subpostmasters Alliance ("JFSA") represents.
The Post Office was contacted for comment.