Seeing actors perform some things he had told the playwright was “cathartic”, he said.
“When I went to watch the rehearsals, I was a bit – dubious is the wrong word – but a bit interested to see how a musical would work with it,” he said.
“We’ve seen a previous play, and then obviously we’ve seen the drama on ITV, and you think, well, how is this going to be handled? And I was absolutely blown away.
“One thing that this will do, which the TV drama didn’t, with the singing, will portray that inner agony, which really comes across.”
Another play on the subject, called Glitch, opened in Reading in June.
In January, Mr Bates vs the Post Office was watched by 10 million people, and has won prizes from the Royal Television Society, National Television Awards and Broadcasting Press Guild.
It also put the issue on the front pages and at the top of the political agenda, with the former government announcing legislation to quash convictions in February.
“I think I got to a position where I thought the drama is not having that kind of impact any more,” O’Hare said.
“But actually, they really did have an impact. They really changed the conversation in the House of Commons. That drama impacted the law, and it felt really encouraging. But I also knew that we were doing something very different.
“In a village hall with a community choir, the experience is wrapped around you, and it’s not about revealing things. It’s actually about trying to heal things and trying to reconnect us all to the story, and reconnect all of us to each other.”
Make Good is on tour until 1 December.