A North East subpostmaster saw his compensation revalued at ten times the initial offer after a legal challenge.
Bob Stevenson, a former subpostmaster from Gateshead, was suspended from his position at East Fellgate Park Post Office in 2002 over an alleged shortfall of £10,000.
An initial compensation offer of £51,200 made to him in May 2023 has now been increased to £502,000.
It comes as lawyers have said Compensation for former subpostmasters was "grossly undervalued" by the Post Office.
Hudgells Solicitors, representing hundreds of subpostmasters, said the Post Office undervalued compensation for those prosecuted, sacked, or made to pay back alleged branch shortfalls.
Mr Stevenson said: "I realised pretty quickly that it simply wasn’t right or fair for me to try and calculate and judge my own compensation application.
"I remember thinking that I needed specialist legal advice, as it was clear there were many hurdles being placed in my way.
"Taking legal advice was the best move I have ever made, as they have taken my compensation from just over £50,000 to more than £500,000."
Mr Stevenson lost his business, house, and was declared bankrupt following his suspension.
He had to sign on for benefits with his wife Carol and take up driving jobs earning £25 a day.
The compensation has now allowed Mr Stevenson and his wife to buy a two-bedroom bungalow after living in a council house for two decades.
Mr Stevenson added: "Without legal support, we’d have had something, but nowhere near what we have been entitled to, and we are so grateful now for that help."
This follows the government opening a new appeals process for those compensated through the Horizon Shortfall Scheme (HSS).
From a sample of 30 cases, Hudgells Solicitors found compensation offers were collectively more than £4.1 million higher, averaging over £137,000 per claim, after being contested.
Neil Hudgell, from Hudgells Solicitors, said almost all cases his firm reviewed were "worryingly undervalued".
He highlighted cases where compensation offers increased from £4,400 to £133,700, from £17,700 to £253,900, and from £21,690 to £238,000 after legal representations.