Welch slotted alongside guitarist Danny Kirwan and keyboard-player and vocalist Christine McVie, the wife of bassist John McVie, who formed the group's eponymous rhythm section with Fleetwood. Over five albums and more trials and tribulations, Welch gave the Mac a new lease of life and paved the way for the arrival of the American songwriting duo Lindsey Buckingham and Stevie Nicks, who helped turned them into superstars.

People magazine might have called Welch's departure in December 1974 "the costliest miscalculation in rock", but his contribution to the Mac's storied career was acknowledged by both fans and his former bandmates. His wonderfully dreamy composition "Sentimental Lady", first recorded with the Mac on the 1972 album Bare Trees, was undoubtedly a harbinger of the soft-rock, radio-friendly sound of Rumours. In 1977, Welch's remake of "Sentimental Lady", featuring Fleetwood, Christine McVie and Buckingham, became the first and biggest of his five US solo hits. Tellingly, it was also the version included on the Mac's 1992 retrospective box-set 25 Years – The Chain.

However, when Fleetwood Mac were inducted into the Rock and Roll Hall of Fame in 1998, Welch wasn't named, even though his tenure matched the length of time served by Green, Spencer or Kirwan, all named in the "main five". "My era was the 'bridge' era. It was a transition. But it was an important period in the history of the band," he told the Cleveland newspaper The Plain Dealer.

"Mick Fleetwood dedicated a whole chapter of his biography to my era of the band. Mick and I co-managed the group for years. I'm the one who brought the band to Los Angeles from England, which put them in the position of hooking up with Lindsey and Stevie. I saw the band through a whole period where they barely survived... Now they want to write me out of the history of the group. It hurts."

Welch partly attributed the snub to the fact that, in 1994, he had sued Fleetwood and the McVies, as well as band attorney Michael Shapiro and Warner Brothers Records, for breach of contract related to underpayment of royalties. Two of the Mac albums he made – 1971's Future Games and 1973's Mystery to Me – had sold half a million copies, and another, Bare Trees, had become a million-seller as new fans explored their back catalogue. But Welch hadn't benefitted as much as the others, who had used their subsequent success to negotiate better terms. The lawsuit was settled in 1996.

Welch always remained on good terms with Buckingham and Nicks and subsequently reconnected with Fleetwood, who remembered him as "a very, very profoundly intelligent human being, always in good humour. He was a huge part of our history. Mostly his legacy would be the songwriting abilities that he brought to Fleetwood Mac, which will survive all of us."

Paying tribute to Welch in a statement, Nicks added: "He was an amazing guitar player. He was funny, sweet and he was smart. I'm so very sorry for his family and for the family of Fleetwood Mac."

Born in 1945, he was the son of movie and TV producer Robert L Welch and actress Templeton Fox. "I grew up in a showbiz environment. Yul Brynner lived across the street," he recalled of his childhood in Beverly Hills.

Musically gifted, he first learned the clarinet but soon picked up a guitar. "I loved all of those guys, Johnny Cash, the Everly Brothers, Elvis Presley, Rick Nelson. I never wanted to be a guitar gunslinger and a star. I just wanted to make that great music," he said.

Something of a Francophile, he talked his parents into sending him to Paris to attend the Sorbonne, though he returned to study French at UCLA. In the mid-Sixties, he joined the interracial R&B group The Seven Souls, who worked with Larry Williams and lost out to Sly and the Family Stone in a battle of the bands. He co-wrote the sublime "I'm No Stranger", which became a northern soul favourite in the UK.

Two years later, he headed back to Paris with fellow Seven Souls Bobby Hunt and Henry Moore. Under the name Head West, the trio made an album for Vogue, though Welch ended up "living on rice and beans and sleeping on the floor. In 1971, I was literally sitting in my underpants in a friend's apartment in Paris. I was wondering what I was gonna do. Maybe head back to L.A.," he said.

Coincidentally, Judy Wong, a former high school girlfriend of his, was working for Fleetwood Mac and suggested him when Spencer departed to join a religious cult, the Children of God. Within days, Welch arrived in London to be picked up by Fleetwood. "He was driving a yellow VW. He was 6ft 6in and weighed about 120 pounds. He was a strange-looking human being."

The drummer took him to Benifold, the Hampshire mansion where the group resided. "It was obvious the Mac had enough money to buy the place, but not to refurbish it," Welch remarked of their UK base until the mid-Seventies. After feeling his way in on Future Games, he really made his presence felt on the Bare Trees album, only for Kirwan to depart under a cloud in August 1972.

Vocalist Dave Walker and guitarist Bob Weston – who died this January – were recruited for 1973's Penguin, but neither lasted long. Worse, following Weston's sacking after his affair with Fleetwood's wife, Jenny Boyd, the Mac cancelled a US tour. Their unscrupulous manager, Clifford Davis, put together a bogus line-up to fulfil the bookings. The move was foiled by tour manager John Courage, yet sidelined the real Mac while lawyers argued over the band's trademark.

The primary Mac songwriter with Christine McVie, Welch rose to the challenge. He had already penned the US radio favourite "Hypnotized" on Mystery to Me, and suggested a move to California to reinvigorate their career. Heroes Are Hard to Find, the first Mac studio album made in Los Angeles, became their best-seller to date in the US, though Welch decided to bow out on a creative high. "After four years of ups and downs, something had to give," said the musician, whose marriage was heading for the rocks, even if his first wife inspired "Sentimental Lady".

In 1975,he formed the short-lived supergroup Paris with ex-members of Jethro Tull and the Nazz. Two years later, he released his million-selling solo debut French Kiss, which also featured the US Top 20 hit "Ebony Eyes", a fusion of rock and disco. In 1981, most of the Mac guested with him at the Roxy in Los Angeles, but his career went into a spin as he fell prey to an "extremely decadent lifestyle." He moved to Nashville with his second wife in the early Nineties. He had experienced health issues and is believed to have taken his own life.

"I just wanted to play guitar in a good band," Welch said in 2003. "I wanted to make the music I love. I wanted to travel the world and have adventures."