Born in Yeovil, Somerset, aged fourteen Cregan joined The Falcons, which was formed whilst he attended Poole Grammar School. After developing his next band The Disastisfied Blues Band, Cregan briefly joined with future Traffic frontman Dave Mason, in Julian Covay and the Machine in 1967 and moved on to join the rock and soul band The Ingoes as a vocalist and guitarist. This band soon morphed into the psychedelic Blossom Toes the same year, who later turned to guitar-led rock.
After recording Julie Driscoll's eponymous album (1969), Cregan joined the soft rock band Stud. The group featured Cregan, John Weider from Family, and also John Wilson and Richard McCracken, the rhythm section from Taste (best known as Rory Gallagher's pre-solo power trio). Stud dissolved when Cregan moved to Family in September 1972, after recording two albums which were released in Germany, where they had their largest audience. He joined Charlie Whitney and Roger Chapman, replacing bassist John Wetton, adapting from rhythm guitar to bass guitar. He toured North America with the band, as the support act for Elton John, in the autumn of 1972. Family recorded two singles and a final album It's Only a Movie (1973). A tour of the UK in the autumn of the same year preceded the demise of the band. Cregan was then briefly reunited with Chapman and Whitney on Chapman Whitney Streetwalkers (1974).
He went on to work with British soul singer Linda Lewis, whom he would later marry. Cregan appears on four of her albums, also assuming a production role on Fathoms deep (1973) and Not A Little Girl Anymore (1975), which gave him the opportunity to work with the Tower of Power horn section.
In October 1974 Cregan was recruited as a guitarist by Steve Harley, as a member of a re-formed Cockney Rebel. Harley and his new Cockney Rebel line-up recorded "Make Me Smile (Come Up and See Me)" (1975) at Abbey Road Studios. The song rose to No. 1 in the UK Singles Chart during 1975. It eventually rose to No. 1 in Europe and Australia as well and featured a guitar break by Cregan, widely believed to have been recorded during a soundcheck. However Cregan's acoustic guitar break was recorded late at night in Abbey Road Studios in several takes. In 1976 he joined Rod Stewart's band and became Stewart's musical director, co-producer and co-writer.
Cregan co-wrote many hits with Stewart, including "Passion" and "Tonight I'm Yours (Don't Hurt Me)", winning the American Society of Composers, Authors and Publishers (ASCAP) award for outstanding songwriting, with each. Cregan was awarded a third ASCAP "outstanding songwriting" award for his co-writing of the song "Forever Young" (1988) and Stewart was awarded a Grammy for his performance of this song. He stayed with Stewart until 1995 after twelve years working together. Cregan has received thirteen multi-platinum awards for his work with Stewart and together they have thirty recorded songs to their joint credit.
In 1990 he spent time writing and producing heavy rock band London Quireboys's Little Bit of What You Fancy (1990) which gave him singles chart success and Canadian rockers Glass Tiger, who achieved international success and platinum selling albums. They were also awarded three Juno Awards, received in Canada. In 1993 Cregan was reunited with Stewart to record "Unplugged...and Seated" which was also filmed by MTV and featured a guest appearance by Ronnie Wood. This recording became Platinum three times in both USA and Canada. In the same year Cregan recorded Van Morrison's song "Have I Told You Lately" (1993) with Stewart, which became a number 1 hit in UK and had top twenty success elsewhere. Cregan's biggest concert appearance with Stewart was on 31 December 1994 at Copacabanain Rio de Janeiro, where they appeared in front of a total estimated audience of over 3.5 million. The Guinness Book of World Records states that this was "the staging of the largest outdoor concert in history".
In 1995 he moved on to form Farm Dogs with Elton John's lyricist Bernie Taupin and they released two albums. During 1997 Cregan started to work with Windham Hill Records as both a producer and musician. Over the next four years he worked as producer and musician with artists such as Janis Ian, Kathleen Keane, Peabo Bryson, Cat Stevens, W.G Snuffy Walden, Grand Drive, Gaelic Storm and Joe Cocker. His work achieved top five hits in different charts and several more platinum selling records. He recorded two platinum selling albums with Katie Melua, Call off the Search (2003) and Piece By Piece (2005), he has also toured extensively with her. Cregan was re-united with Roger Chapman in 2005, at first for live performances and then to produce Chapman's solo album One More Time For Peace (2007).
In 2008, Cregan formed Creative Music Management with renowned music business lawyer Robert W. Allan. Together they manage young singer songwriter, Charlie Hole. His first album "The Joy of a Caged Bird" produced and recorded by Cregan, was released in Dec 2012 on Cocomack records. Charlie has signed an International publishing deal with Rondor/Universal Music in Los Angeles and Fujipacific in Japan.
In 2011, he decided, for the first time, to form his own band, Cregan & Co. This gave him the opportunity to play live the songs he had written, recorded and co-produced with Rod Stewart. In January 2013, Roger Chapman agreed to reform Family for two concerts in London at the Empire Shepherd's Bush. This coincided with Family winning Classic Rock magazine's "Spirit of Progressive Rock" Award. He also joined a reformed Family for the group's final shows in late 2016, part of a line up that only included Chapman, Poli Palmer and Cregan from the band's 60s and 70s output.
On 13 September 2015, Cregan joined Rod Stewart on stage at the BBC Radio 2 'Live in Hyde Park London' Festival.
Blossom ToesWe Are Ever So Clean (1967)
If Only for a Moment (1969)
Julie Driscoll1969 (1971)
Cat StevensSaturnight (1974)
Shawn PhillipsSecond Contribution (1971)
Goodbye Live at Command (1973)
FamilyIt's Only a Movie (1973)
Linda LewisLark (1972)
Fathoms Deep (1973)
Not a Little Girl Anymore (1975)
Woman Overboard (1977)
StreetwalkersChapman Whitney Streetwalkers (1974)
Murray HeadSay It Ain't So (1976)
Steve Harley & Cockney Rebel"Make Me Smile (Come Up and See Me)" (1975)
Timeless Flight (1976)
Love's a Prima Donna (1976)
Face to Face: A Live Recording (1977)
Hobo with a Grin (1978)
Rod StewartFoot Loose & Fancy Free (1977)
Blondes Have More Fun (1978)
Foolish Behaviour (1980)
Tonight I'm Yours (1981)
Body Wishes (1983)
Every Beat of My Heart (1986)
Out of Order also as producer. (1988)
Storyteller - The Complete Anthology: 1964–1990 (1989)
Vagabond Heart (1991)
Unplugged...and Seated (1993)
A Spanner in the Works (1995)
Bruce RobertsBruce Roberts (1978)
Mike BattTarot Suite (1979)
Rita CoolidgeLove Lessons (1992)
Glass TigerAir Time: The Best of Glass Tiger as producer. (1993)
Farm DogsLast Stand in Open Country (1996)
Immigrant Sons (1998)
Katie MeluaCall off the Search Dramatico (2003)
"Closest Thing to Crazy" (2003)
Piece by Piece Dramatico (2005)
London Quireboys"Little Bit of What You Fancy" as producer. Capitol Records (1990)
Roger ChapmanOne More Time For Peace as producer. (2007)
Various artistsTribute to Curtis Mayfield with Rod Stewart. (1994)
Cregan married Hollywood, California model Jane Booke and they lived in Los Angeles. Recently Cregan has spent more time in London. On Steve Harley's BBC Radio 2 show aired in January 2004, he explained that he had grown tired of Los Angeles culture and has moved to UK.