Inside and outside the ring with former Boston boxer Sean Mannion

Sean Mannion is a former Boston boxer who is the subject of the documentary “Rocky Ros Muc.” The documentary makes its world premiere Saturday at 6 p.m. at the Somerville Theatre as part of Boston’s Irish Film Festival.

The fights never did get to him. Not the handful of bouts in Atlantic City. Not the 1984 world title fight at Madison Square Garden, at the time pro boxing’s grandest stage.

Nervous? Sean Mannion?

“Never, never, never,” he says.

But the debut this weekend of a new documentary about his life — “Rocky Ros Muc,” which makes its world premiere Saturday at the Somerville Theatre as part of Boston’s Irish Film Festival — that has thrust him back, at least temporarily, into the local spotlight?

“Things like this make me nervous,” the 60-year-old former boxer said this week, his Gaelic accent still thick. “I don’t know why.”

As documentary subjects go, you could do plenty worse than Mannion.

A native of the small village of Ros Muc in Galway, he immigrated to Boston as a teenager in the 1970s, eventually finding his way into pro boxing. His sparring partners were often members of Whitey Bulger’s Winter Hill gang. And in 1984, he nearly reached boxing’s pinnacle, fighting for the World Boxing Association junior middleweight title, in a match the southpaw would lose to Mike McCallum.

But while the film is ostensibly about Mannion’s unlikely rise through the US boxing ranks, it also explores a range of deeper themes: immigration, community, identity.

“What I wanted to do as a filmmaker was expand [Sean’s] story beyond sport,” says Michael Fanning, the film’s director/producer. “It seemed like a quintessential Irish-American story. It had sport, it had politics, it had the Irish language, it was a story about Boston and Ireland.

“It had so many layers to it.”

Part of the film, for instance, focuses on the idea of home — and the experience of the many Irish immigrants who had settled in Boston at the time.

Among the things for which Mannion was known was a deep loyalty to his home country. He took pride in speaking Gaelic and once turned down $25,000 to wear a boxing brand’s logo on his trunks — so that he could instead display the name of his hometown in Ireland.

“As a 9 year old, I remember Sean fighting for the world title and being in awe of him when I met him when he returned to Ireland shortly afterwards,” said Rónán Mac Con Iomaire, whose book, “Rocky Ros Muc” chronicles Mannion’s life and also serves as the inspiration for the new documentary.

“It was a big deal for us to have one of our own from Connemara, one of the most isolated and deprived areas in Ireland, and where Irish [Gaelic] is still the first language, on the world stage.”

Iroh

The film, certainly, highlights the Irish-American connection. It was filmed in both Ireland and the United States, in both English and Gaelic, and includes interviews with, among others, Boston Mayor Martin J. Walsh.

Completed just after Christmas, it was a 3½-year project.

“When I met Sean for the first time, I realized just how good the film could be,” Fanning says. “Sean’s a very humble man; he doesn’t like to brag or boast about his accomplishments. You almost have to find out what happened from other people.”

Nerves aside, Mannion spoke highly of the filmmaking process as well.

In a phone interview this week, the current Billerica resident mentioned that he’d yet to see the final product — though the filmmakers had offered to send him a DVD of the film ahead of Saturday’s 6 p.m. premiere, and he was looking forward to firing it up upon its arrival.

“They want me to see it before it comes out on Saturday,” he joked. “In case I get a heart attack.”