Kirwan's arrival expanded Fleetwood Mac to a five-piece with three guitarists, Danny playing alongside renowned ex-Bluesbreaker Green, and slide guitar player Jeremy Spencer, plus experienced bassist John McVie and drummer Fleetwood, both also formerly with the Bluesbreakers. Green had been looking for another guitarist to share some of the workload, in view of Spencer being unwilling to contribute much to Green's songs.
In an interview with Mike Vernon in June 1999, 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." He added that in those early days, Kirwan "was so into it that he cried as he played".
The UK release of Then Play On featured two extra, slightly older, Kirwan recordings—the rather morose "Without You", and the heavy "One Sunny Day". The US-only release English Rose from the same era included these two songs, plus the tense blues "Something Inside of Me" and the aforementioned "Jigsaw Puzzle Blues", both also dating from earlier sessions.
When the US track listing of Then Play On was reordered to allow the inclusion of the full version of Green's hit single "Oh Well", two of Kirwan's songs ("My Dream" and "When You Say") were dropped. Only "Coming Your Way", the wistful "Although the Sun Is Shining", and his duet with Green "Like Crying" appeared on all the later non-UK vinyl releases. On the CD release, Kirwan's two dropped songs were reinstated, although "One Sunny Day" and "Without You" were now absent from releases in all territories, including the UK.
Out-take packages from this era, such as the Vaudeville Years and Show-Biz Blues double sets, include many more Kirwan songs, showing blues influences as well as the more arcane tastes that led to songs like "Tell Me from the Start" which could have been mistaken for the 1920s-style group The Temperance Seven. Such unusual musical interests prompted band leader Green to dub Kirwan "Ragtime Cowboy Joe"—at least that was preferable to Green's other name for him, "Young Eyes", which Kirwan was less keen on.
Although Fleetwood Mac's hit singles from 1969–70 were all Green-penned tunes, Kirwan's style showed through thanks to Green's increasing desire not to act as the band's main focus. He took the solo on "Oh Well Pt. 1" and joined Green in the dual guitar harmonies on "Albatross". The final hit single from this line-up, "The Green Manalishi", also provided Kirwan with opportunity to step forward, although Green generally stole the show. The B-side of this single was the instrumental "World in Harmony", the only track ever to receive a "Kirwan/Green" joint songwriting credit.
Kirwan also worked on the first solo album from a then-current member of Fleetwood Mac, when Jeremy Spencer released his eponymously titled album in 1970. Kirwan played rhythm guitar and sang backing vocals throughout. The album was not commercially successful but Spencer discovered that he and Kirwan worked well together without Green: "In retrospect, one of the most enjoyable things was working with Danny on it, as it brought out a side of him I hadn't seen."
Kirwan was also asked to contribute as a session guitarist with the blues band Tramp on their album Tramp (1969). After he left Fleetwood Mac, Kirwan worked with Tramp again on their second album, Put a Record On (1974), and also with Chris Youlden of Savoy Brown on his solo album Nowhere Road (1973).
Kirwan's songs on the album included "Station Man" (co-written with Spencer and John McVie) which became a live staple for some years, stretching into the post-1974 Buckingham-Nicks era. His other songs were "Jewel-Eyed Judy", dedicated to a friend of the band, Judy Wong; the energetic "Tell Me All the Things You Do", and "Earl Gray", an atmospheric instrumental which Kirwan largely composed while Peter Green was still in the band. Kirwan could also be heard providing distinctive backing vocals to some of Spencer's numbers, such as the 1950s-flavoured album opener, "This Is the Rock".
Other Kirwan compositions from the second half of 1970, such as those that eventually surfaced on the 2003 Madison Blues CD box set, included "Down at the Crown", with lyrics centring on a pub down the lane from the communal band house 'Benifold' in Headley, Hampshire. The unsuccessful single "Dragonfly", recorded late in the year, was also written by Kirwan, and included lyrics adapted from a poem by W. H. Davies. Peter Green said of "Dragonfly", "The best thing he ever wrote... that should have been a hit." This was not to be the last time Kirwan used a poem as lyrics for a song, and may have been a solution to Kirwan's apparent occasional lack of inspiration when writing lyrics. The B-side of the single, "The Purple Dancer", was a co-written effort uniquely featuring both Kirwan and Spencer on lead vocals.
The last two Fleetwood Mac albums to feature Kirwan showed an increasing maturity in his songwriting and playing, his songs taking up about half of each album. His guitar work also showed noticeably in several songs written by Welch and McVie, as they developed their own songwriting techniques.
Future Games (1971) was a departure from its predecessor with the clear absence of Spencer and his 50s rock 'n' roll parodies. Welch brought a couple of new songs, notably the lengthy title track, which featured both guitarists stretching out. Kirwan contributed the opener "Woman of 1000 Years" which, according to one unknown critic at the time, "floated on a languid sea of echo-laden acoustic and electric guitars". His other songs were the melodic "Sands of Time" which was chosen as a single in the USA, and the country-flavoured "Sometimes" which suggested the route he would take during his solo career. Kirwan's influence can also clearly be heard on the two Christine McVie songs, "Morning Rain" and the laid-back and gentle "Show Me a Smile".
Bare Trees (1972) contained five Kirwan songs including another instrumental, "Sunny Side of Heaven", and the album-closer "Dust" with its lyric taken from a romantic poem by British war poet Rupert Brooke, although Brooke was not credited. "Danny's Chant" featured heavy use of the wah-wah guitar effect and was effectively an instrumental but for Kirwan's wordless scat vocals. "Child of Mine", which touched upon the absence of Kirwan's father during his childhood, and "Bare Trees" opened each side of the LP and showed funk and slight jazz leanings. An unused Kirwan track, "Trinity", was played live for a period during 1972 and the studio version was eventually released on the 1992 box set 25 Years - The Chain.
Kirwan's reaction was initially one of surprise, and it seemed he had little idea of how alienated from the other band members he had become, but shortly afterwards he met up with his replacement Bob Weston, of which Weston stated: "He was aware that I was taking over, and rather sarcastically wished me the best of luck - then paused and added "You're gonna need it". I read between the lines that he was pretty angry with the band."
1976's Midnight in San Juan featured a reggae-inspired cover of The Beatles' "Let It Be", which was released as a single in the USA. Otherwise, Kirwan tended towards the simple tunes and they arguably benefitted from the absence of the slightly cloying production on the previous LP. Lyrically the subject matter still largely dwelt upon love, but apparently less cheerfully than before, with growing themes of loneliness and isolation, such as on the closing track "Castaway". There was also a song, "Look Around You", written by another Mac refugee, Dave Walker, with whom Kirwan had very briefly formed a band called Hungry Fighter in 1974.
Kirwan's last album, Hello There Big Boy!, ironically featured guitar contributions by his Fleetwood Mac replacement, Bob Weston. Kirwan was not well at this time and it is not clear how much guitar work he contributed to the recording, though he did sing on all the tracks. Far fewer of the songs were self-penned, and there was one song dug up from his Fleetwood Mac days. There were also backing vocalists for the first time, and musical style was much less distinct. Producer Clifford Davis added the contribution of 87 musicians to the final recording, and later described the album as "so bad".
None of Kirwan's solo releases was commercially successful. This can be largely attributed to his total reluctance to perform live. Kirwan did not play any live gigs after a few shows with Tramp and a one-off outing with Hungry Fighter (all in 1974), leaving all three of his solo albums completely unsupported by any form of extra exposure or active promotion apart from an irregular string of equally unsuccessful singles. None of his solo work saw release in continental Europe, which might have been a source of success given Peter Green's resurgence there, particularly in Germany.
Kirwan was married in 1971, but was divorced a few years later, and he has one son.
During the late 1970s Kirwan's health deteriorated significantly and since then he has played no further part in the music industry. During the 1980s and 1990s, he endured a period of homelessness living in London.
His three solo albums were given a very belated CD release in February 2006, but only in Japan. A limited edition of 2,500 copies of "Second Chapter" was issued by Repertoire Records in early 2008. The rights/royalties situation regarding these releases is currently such that it is not commonly known if Kirwan will see any income from them. Prior to this, only Second Chapter had been available on CD, for a brief period in Germany in 1993.
During the past couple of years, there have been rumours of a reunion of the early line-up of Fleetwood Mac, involving Green and Spencer. Whilst these two guitarists apparently remain unconvinced of the merits of such a project, Kirwan has remained as silent as ever on the subject. In April 2006, during a question-and-answer session on the Penguin Fleetwood Mac fan website, bass player John McVie said of the reunion idea:
"Albatross", "Need Your Love So Bad" and "Oh Well" were also re-released in various European markets with different B-sides. "Somebody's Gonna Get Their Head Kicked in Tonight" was credited to 'Earl Vince and the Valiants', a sometime pseudonym of Fleetwood Mac while in 'Jeremy Spencer 50s mode'.
Fleetwood Mac's "Man of the World" was also released in the UK with Danny Kirwan's "Second Chapter" on the B-side, both on the DJM label and on Epic. In the USA, Kirwan's "Best Girl in the World" was the B-side, this time only on DJM.
Christine Perfect was Christine McVie's maiden name.