Daniel David Kirwan (né Langran, 13 May 1950 – 8 June 2018) was a British musician and guitarist, singer and songwriter with the blues-rock band Fleetwood Mac between 1968 and 1972. He released three albums as a solo artist from 1975 to 1979, recorded albums with Otis Spann, Chris Youlden, and Tramp, and worked with former Fleetwood Mac colleagues Jeremy Spencer and Christine McVie on some of their solo projects. He was inducted into the Rock and Roll Hall of Fame as a member of Fleetwood Mac in 1998.

Kirwan was born Daniel David Langran on 13 May 1950 and raised in Brixton, South London. His parents separated when he was young and his mother, Phyllis Rose Langran, married Aloysious J. Kirwan in 1958 when Danny was eight. Kirwan left school in 1967 with six O-levels and worked for a year as an insurance clerk in Fenchurch Street in the City of London.

Kirwan's mother was a singer and he grew up listening to the music of jazz musicians such as Eddie Lang, Joe Venuti, Belgian gypsy guitarist Django Reinhardt and 1930s–40s groups such as the Ink Spots. He began learning guitar at the age of 15 and rapidly became an accomplished musician and guitarist. He was influenced by, among others, Hank Marvin of the Shadows, Django Reinhardt, Jimi Hendrix, and particularly by Eric Clapton's playing in the Bluesbreakers. Kirwan was 17 when he came to the attention of established British blues band Fleetwood Mac in London while fronting his first band, Boilerhouse, a blues three-piece with Trevor Stevens on bass and Dave Terrey on drums. Boilerhouse played support slots for Fleetwood Mac at London venues such as the Nag's Head in Battersea and John Gee's Marquee Club in Wardour Street.

Mick Fleetwood recalled, "We met Danny at a little club in Brixton, the Nag's Head, one night when we played with a local band called Boilerhouse. Danny played beautifully, getting a subtle tremolo effect from his fingering." Fleetwood Mac's producer Mike Vernon booked Boilerhouse to play at his blues club, the Blue Horizon in Battersea, and he remembered, "Danny was outstanding. He played with an almost scary intensity. He had a guitar style that wasn't like anyone else I'd heard in England." Kirwan became a devoted fan of the band's lead guitarist, Peter Green, and followed Fleetwood Mac around the London clubs, often turning up at gigs during the afternoon to help to carry the gear in and jam with Green after the soundcheck. "Which is how Danny Kirwan came into our lives," Fleetwood said. "Danny was a huge fan of Peter's. He would see us every chance he got, usually watching in awe from the front row."

Fleetwood Mac had been constituted as a quartet but Green, the band's founder, wanted to move away from pure blues and had been looking for a new musical collaborator and backing guitarist to work with, as slide guitarist Jeremy Spencer did not contribute to his songs. Green found that he and Kirwan worked well together, and suggested to Fleetwood that Kirwan could join Fleetwood Mac. Although the rest of the band were not entirely convinced, Fleetwood invited Kirwan to join the band in August 1968. Fleetwood said, "Danny was an exceptional guitar player. It was clear that he needed to be with better players ... In the end, we just invited him to join us. It was one of those 'ah-ha' moments when you realise the answer is right there in front of you." Kirwan's reaction was described as "astonishment and delight". His arrival expanded Fleetwood Mac to a five-piece with three guitarists.

Green described Kirwan as "a clever boy who got ideas for his guitar playing by listening to all that old-fashioned Roaring Twenties big-band stuff." Kirwan was known to be "emotionally fragile", and Green said that in the early days, Kirwan "was so into it that he cried as he played."

A year after forming Fleetwood Mac, Peter Green was looking for ways to extend the band and perhaps change its direction. He wanted to be open to other musical styles and bring in more of his own material. Kirwan was the ideal foil for Green's new approach: he played gentle, supportive rhythm guitar to Green and Spencer's fiery solo work and introduced vocal harmonies to some of the songs. Spencer said, "Peter and I had seen Danny play and thought he was very good. Peter and Danny worked well together."

Fleetwood said, "Danny worked out great from the start. His playing was always very melodic and tuneful, with lots of bent notes and vibrato. Danny's style of playing complemented Peter's perfectly because he was already a disciple. His sense of melody on rhythm guitar really drew Peter out, allowing him to write songs in a different style. He was full of ideas that helped to move Fleetwood Mac out of the blues and into the rock mainstream ... Playing live, he was a madman." Fleetwood Mac biographer Leah Furman said Kirwan had "provided a perfect sounding board for Peter's ideas, added stylistic texture, and moved Fleetwood Mac away from pure blues."