Inspired heavily by Meic Stevens, Gai began writing songs while at Dolgellau college. Mim Twm Llai started in 1996, when the various members of Anweledig were scattered across the country. While at Aberystwyth University, Gai began performing at various venues around the town, and was invited to play on the S4C show Garej.

Although Gai plays the majority of instruments on Mim Twn Llai's songs, he is joined live and on record by a variety of other performers. They include drummer Phil Jones, who performed the band's early songs with Gai at their local pub, The Tap in Tanygrisiau, Blaenau Ffestiniog. Indeed, the people of the town and local community are inspirations for many of the songs.

Mim Twm Llai performed at Super Furry Animals' Pesda Roc show in 2003. They've recorded two albums for Crai - 2002's O'r Sbensh, which won Album Of The Year at Radio Cymru's 2003 rock and pop awards, and 2005's Straeon Y Cymdogion.

And the name?  Well, his father Meurig Thomas was known as Mim Twm. Gai's eldest sister Elaine was known as Mim Twm Bach, which made Gai Mim Twm Llai - the smaller Mim Twm.