But starting in 2017, he struggled through several health issues.
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"I had 11 different surgeries over the course of 15 months and the doctors say all the anesthesia that was in my system eventually took its toll on my kidneys," said Fr. O'Sullivan.
He was on dialysis for five years.
In November, he wrote a letter in the church bulletin, explaining that he was searching for a kidney donor.
"A couple people in the parish did call but were not qualified for some reason or another," he said. "And then nothing came of it until January."
On Wednesday, Fr. O'Sullivan was finally able to hug the mother of his kidney donor for the first time.
He and Rosemarie Frankel shared a tearful embrace at the church rectory.
"Big guy, huge personality, had a laugh that could light up a room," said Christine Moretti of Bensalem, talking about her big brother.
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Albert Stanley, 46, of South Philadelphia, suffered several strokes and a brain bleed around the holidays and died on New Year's Day.
"I had to look at his license and see if he was an organ donor," said Moretti. "It does not surprise me that he was."
Moretti is a parishioner at St. Ephrem's and got in touch with Father O'Sullivan on January 2.
"He had multiple people in his family that were not matches, so in speaking with him, of course, this would be the miracle that we need," said Moretti, fighting back tears.
On January 3, O'Sullivan got the call: Stanley was a match.
"I remember driving on the turnpike thinking, 'in 12 hours I'm going to be in surgery,'" he said.
Father O'Sullivan received both of Stanley's kidneys and is no longer on dialysis.
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"It's humbling that they made such an extraordinary decision, a very generous decision, even in the midst of a mother's worst grief," he said.
Stanley's family said knowing his organs saved others has given them comfort in a time of unimaginable and unexpected loss.
"It was already a comfort knowing that he would live on through others. But to know that it's someone so close -- part of our parish, that my kids interact with -- was very meaningful to me," said Moretti.
Stanley's family says his lungs and corneas were also donated to other recipients.
They hope others will consider organ donation and hope to become involved with the Sharing Network Foundation, the organization that helped them through the process.
As for Father O'Sullivan, he's still recovering and hopes to be back to saying Mass at St. Ephrem in April.