According to the BBC, Mostly Autumn "fuse the music of Genesis and Pink Floyd with Celtic themes, hard rock and strong, emotional melodies".

The band's founding line-up consisted of band leader Bryan Josh (vocals and guitars), Heidi Widdop (vocals), Iain Jennings (keyboards), Liam Davison (guitars), Alun Hughes (bass and occasional keyboards), Bob Faulds (violin), Kev Gibbons (whistles), and Chris Walton (drums).

Mostly Autumn's original rhythm section of Alun Hughes and Chris Walton left the band during 1996 to concentrate on other musical projects and family commitments respectively.

By 1999, when the band recorded its second album, The Spirit of Autumn Past, Gibbons and Scott had been replaced by Angela Goldthorpe and Rob McNeil respectively.

In 2000 (as a three piece – Josh, Findlay, and Goldthorpe) they achieved a support slot for Blackmore's Night on their Under a Violet Moon tour, bringing them to a wider audience.

On the cover artwork for the following Blackmore's Night album Fires at Midnight (2001), Heather Findlay provided the illustration for the song "Hanging Tree".

[citation needed] Chris Johnson was then recruited as a permanent replacement, with Angela (now under her married name Gordon) also taking a more prominent role on keyboards.

Ex-Karnataka drummer Gavin Griffiths stood in on drums for most of the 2007 live shows; Andrew Jennings temporarily rejoined the group at the end of 2007, until Henry Bourne took over in 2008.

Anne-Marie Helder (who had played support slots in the past and stood in for Angela during her pregnancy) took over the role of flute, keyboards and backing vocals.

[11] From mid-2013 onwards, Helder and Griffiths were absent from the band's touring line-up due to other commitments; their positions being temporarily filled by keyboardist Hannah Hird and drummer Alex Cromarty.

[20] Founding members Bryan Josh, Liam Davison, Heidi Widdop, Alun Hughes, Bob Faulds and Chris Walton played in the Pink Floyd/1970s tribute band One Stoned Snowman.

He recruited then-Mostly Autumn backing vocalist Olivia Sparnenn to sing lead vocals and the pair, along with various other musicians recorded three albums.

During 2005 Heather Findlay and Angela Gordon formed an acoustic side project called Odin Dragonfly (an anagram of their surnames), making live appearances both as a support act and as headliners.