He was born in Wye, Kent, was educated at Bedales and the Royal College of Music. Tobias formed Trees in 1969 with Celia Humphris on vocals, Barry Clarke on lead guitar, Unwin Brown on drums/vocals & David Costa on acoustic guitar & dulcimer. Bias sang and played bass, guitar and piano on their two CBS albums, The Garden of Jane Delawney (1970) and On the Shore (1971), and wrote much of their material. "On the Shore" was remastered in January 2007 and re released on CD.
In the 1980s, Boshell became a guest musician for Barclay James Harvest, touring and recording with them. After he ceased to be a guest musician for Barclay James Harvest in 1987, he then moved on to The Moody Blues, becoming their lead keyboard player after the departure of Patrick Moraz in 1991. He stayed with the Moody Blues until their 2001 tour. He has also recorded with Sheena Easton, Kevin Ayers, Beverley Craven, Chris Farlowe, and Duane Eddy.