But Fr D'Arcy, a broadcaster and newspaper columnist, was censured by the Vatican in April 2012.
From then on, it is understood his newspaper column was run past a Church censor.
The documentary that he calls "a serious audit" of his life could change the course of that life.
"Will I still be allowed to remain a priest once the documentary has been transmitted?" he asked.
In the past, Fr D'Arcy has spoken out against mandatory celibacy for priests, church teaching on contraception and has been a vocal critic of the handling of clerical sexual abuse.
In the wake of the Murphy Report into clerical abuse in the Archdiocese of Dublin in the Republic of Ireland, Fr D'Arcy called for reformation of church structures and accused the Holy See of using legal procedures to shield itself from criticism over its handling of abuse.
The BBC did not know about the Vatican censorship at the time when the approach for the documentary was made, he said.
His decision to take part in the film was one which he spent months agonising over.
"I wasn't doing it for publicity. Forty years in the public eye is more than enough," he said.
And when he was censored, he found that he had a fresh question to ask himself. "How can I stay in a Church which I've served for 50 years and which now doesn't trust me to speak my mind about religion?" he asked.
Fr D'Arcy said he decided to make the documentary covering his life in the priesthood because he wanted to be open about his ministry.
The journey brought him into contact with those who thought the Vatican was correct to censor him and those who wanted him to be more vocal and challenge Church suppression on behalf of a bewildered laity.
It proved an arduous journey.
"By now I'm exhausted, vulnerable, anxious and yet deeply satisfied that I made the journey in such a public way," he said.
"No matter how it turns out, I know I've been truly open and no-one can say I'm leading a double life."
But once the programme is aired, will he be allowed to continue as a priest?
"That's another question altogether and is outside my control," he said.
The Turbulent Priest in on BBC One NI on Monday 29 October at 22:35 BST