Mulholland's first posting was as a Procurator Fiscal Depute at Greenock, before being transferred to the same post at Glasgow in 1987. He remained there until 1991, when he was transferred to the Crown Office, working as a solicitor in the High Court Unit. He became a Notary Public (NP) in 1992 and joined the Society of Solicitors in the Supreme Courts of Scotland in 1993. In 1994, he moved from the Crown Office's High Court Unit to its Appeals Unit, and in 1995 qualified as a solicitor-advocate.