Bass was born on 30 January 1771 at Aswarby, near Sleaford, Lincolnshire. His father, George, was a tenant farmer, George Bass, and his mother a local beauty named Sarah (née Newman). His father died in 1777. He went to Boston Grammar School and later studied medicine at the hospital in Boston, Lincolnshire. At the age of 18, he was accepted in London as a member of the Company of Surgeons, and in 1794 he joined the Royal Navy as a surgeon.