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The 29-year-old will face world number one Novak Djokovic in Sunday's final after beating defending champion Stan Wawrinka 6-4 6-2 4-6 6-2.
"Reaching the French Open final is definitely not something I thought I'd do," he told BBC Radio 5 live.
"When I was having problems with my back on clay, I never thought it would happen for me here."
He added: "Last year, I started to have the belief that I could do it. It's great credit to my team to get my body healthy."
Murray has now reached the final of all four Grand Slam tournaments.
But up until 2013, the year he had surgery on a back injury, he had reached the semi-finals at Roland Garros just once.
The world number two made the final four in 2014 and 2015 - going out to Djokovic last year - but has been in impressive form on clay this season, winning 18 of 20 matches on the surface.
Djokovic, 29, who has won every Grand Slam except the French Open, holds a substantial 23-10 lead in his career head-to-head with Murray.
But the Scot won their last meeting, beating the Serb on clay in the final of the Rome Masters.
BBC Radio 5 live commentator and 1987 Wimbledon winner Pat Cash suggested the damp conditions in Paris may favour Murray.
But Murray insisted Djokovic "plays well on all the courts".
He added: "It probably means there will be long rallies, you have to be patient in these conditions. It's not easy to hit winners."
Djokovic has made three of the last four French Open finals but lost them all.
"I'm sure it's going to be a final with a lot of emotions and exchanges from the baseline because we have a similar style of game," he said.
"I know his game he knows mine. I'm sure we'll both give it our all."
Murray was seen chatting with former Manchester United and France striker Eric Cantona after his semi-final victory.
It seems Murray may have arranged himself a teaching job for later in the summer.
"We mainly spoke about football," said Murray. "He said he's just had three tennis lessons. I told him if he's ever around the Wimbledon area I'd take him for a lesson at Wimbledon."
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British number one Andy Murray has said there was a time he thought he would never reach a French Open final.