After the man sat down at a piano and leaned into the microphone, his first words were a declaration: “Sedaka’s back … again!”

It was late March and the lounge at Vitello’s — an old-school Italian restaurant in Studio City, California — was packed for a show by the irrepressible 86-year-old singer and songwriter Neil Sedaka. He had booked a series of Sunday night appearances there to mark the golden anniversary of his professional resurrection.

Fifty years ago, Sedaka completed one of the most remarkable comebacks in pop music. A smiling star of the teen idol era, he’d made his name with run of hummable hits — “Oh Carol,” “Calendar Girl,” “Happy Birthday Sweet Sixteen,” “Breaking Up Is Hard to Do” — but his bubbly tunes, sung in a high tenor, were soon swept away, first by the arrival of the Beatles and then by the turmoil of the 1960s.

In the difficult years that followed, Sedaka lost his fortune, his record deal and his sense of self. At his lowest, he would walk down the street and people would ask: “Didn’t you used to be Neil Sedaka?”

In the early ’70s, Sedaka exiled himself to England, where he gradually rebuilt his career, playing small clubs as he rediscovered his muse and a new group of collaborators. A fellow piano man and avowed fan, Elton John, eventually midwifed his return to the American charts in 1975, helping release the hit LP “Sedaka’s Back,” which was recently reissued in a deluxe vinyl package.

Onstage at Vitello’s, Sedaka introduced the songs that heralded his second coming — “Laughter in the Rain,” “Bad Blood,” “Love Will Keep Us Together” — and beamed as he recounted his journey from the top to the bottom and back again.

“You see,” he said, a note of pride in his lilting Brooklyn accent, “I’m a survivor.”

On a sunny summer morning a few weeks later, Sedaka settled into his office in the West Hollywood, California, apartment that he and his wife of nearly 63 years, Leba, have called home since 1976, for an interview. He remains a furious ball of showbiz energy, telling stories, dropping names and singing snatches of his songs with an infectious zeal.

It was a combination of precocious charm and prodigious talent that landed Sedaka a scholarship to Juilliard, but he gave up his classical pursuits after hearing the Penguins’ 1954 hit “Earth Angel,” and instead learned his trade as a pop songwriter.

Along with his songwriting partner Howie Greenfield, Sedaka wrote the Connie Francis hit “Stupid Cupid,” before stepping out as a solo artist, making the Top 20 with “The Diary” in 1958. Over the next five years, Sedaka sired a succession of smashes, becoming RCA’s second biggest star behind Elvis Presley. But his fortunes started to wane in 1963, and in 1966, the label dropped him. Worse, he discovered that his mother’s boyfriend, who had been managing him, had run through his savings.

Sedaka was back to plugging his songs and playing piano on other artist’s recording sessions. “I would come into a session, and they would say, ‘Neil Sedaka?! What are you doing here?’ ” he recalled. “But I had a wife and two kids, so every penny counted. And it was still a way of expressing myself as a musician.”

The latter half of the ’60s saw Sedaka effectively sidelined as pop rapidly evolved from beat music to psychedelia, country-rock to the singer-songwriter movement. “I missed it. I missed it with a vengeance,” he said. “I listened to the radio and thought what do I have to do? No more of the tra-la-las and do-be-dos, which I was the king of. I wanted to be an artist that fit into the culture of the time.”

His first attempt at a comeback, the 1971 singer- songwriter collection “Emergence,” flopped. At the suggestion of his booking agent, Sedaka moved to England that fall, where he could earn a living playing a circuit of working men’s clubs. “I sang all the old hits for them, that’s all they knew,” he said. “But the people were very nice, so I started to put some of the new songs in.”

At the Batley Variety Club near Leeds, Sedaka was approached by music manager Harvey Lisberg with an offer to work up material at Strawberry Studios, where his clients — Graham Gouldman, Lol Crème, Kevin Godley and Eric Stewart, soon to become the hit pop band 10cc — could back him, in hopes of reviving his recording career.

The Sedaka/10cc collaboration produced immediate chemistry, and a couple of hit albums in the U.K., including “Solitaire” from 1972 and “The Tra-La Days Are Over” the next year. Gaining momentum, he was soon playing bigger venues in England, though he remained without a U.S. label. Fate intervened backstage at a Bee Gees concert when Sedaka met Elton John.

“He told me he was a big fan, that he’d bought all my early records,” Sedaka said. A few days later John turned up at Sedaka’s apartment. “Elton came in dressed in all his regalia, and he sat and played, ‘Don’t Let the Sun Go Down on Me,’ which he’d just written. Then he asked: ‘What have you been doing?’ and I played him ‘Laughter in the Rain.’ He said, ‘That’s a hit! We’ve got to get you on my label.’ ”

John’s company compiled the best of his recent albums on “Sedaka’s Back,” as the star began a personal campaign on Sedaka’s behalf. “I was so committed to relaunching his career,” John recalled in 2009, “that he used to call me ‘the most expensive publicist in the world!’ ”

In early 1975, “Laughter in the Rain” reached No. 1 in the United States. After 12 long years, he was back on top of the charts, on top of the world, kick-starting a triumphant year that included the Captain & Tennille’s version of “Love Will Keep Us Together” rising to become a Grammy winner. “It was a wonderful moment,” he said, as his eyes glistened at the memory.

Last year, Primary Wave announced it had made a deal with Sedaka for his publishing and master album rights. In addition to the reissue of “Sedaka’s Back,” there are plans for other expanded physical releases and efforts to bring albums like “The Hungry Years” (1976) to streaming services for the first time.

One thing the Primary Wave campaign won’t include is any new material from Sedaka, who stopped writing a few years ago. “I wrote songs from the time I was 13 years old until I was 83 years old,” he said and shrugged. “I figure if you can’t top what you’ve done before, don’t do it anymore.”

In the end, Sedaka doesn’t seem worried about his legacy. “I was born to make music, that was my purpose in life — to spread joy, and to make myself happy,” he said, smiling. “And I’ve done that.”