Greg was first admitted as a solicitor on 10 July 1981 and was given an unqualified practising certificate to enable him to commence immediately with Harold Wanstall at his practice at Kogarah opposite the Court House. They practised as partners for about 12 months under the firm name H.E. Wanstall Johnston & Co. Thereafter until he was called to the bar on 4 November 1988 Greg practised as a sole practitioner at Kogarah under the firm name Gregory M. Johnston & Co. Greg had a wide practice including Family Law, Conveyancing, Probate, Criminal Law, Common Law and Local Government Law.
Greg was called to the bar on 4 November 1988. It was not long before Greg was engaged in Family Law and De Facto Law work exclusively. Greg is now in his 30th year at the bar and is also an experienced mediator of Family Law disputes and has been a member of the Australian Institute of Family Law Arbitrators and Mediators since 1994. He is a member of the Family Law Section of the Law Council of Australia since 1992 and the Australian Property Institute since 1972. He has also qualified as a Family Law Arbitrator.
Greg has appeared in many leading reported cases including Black and Kellner (1992) FLC 92-287 both at first instance and on appeal (which significantly developed the law of full and frank disclosure in financial proceedings), Georgeson and Georgeson (1995) FLC 92-618 – both at first instance and on appeal (developing to law relating to minority interests in private corporations), A and A: Relocation Approach (2000) FLC 93-035 (relocation of children) and Bolitho and Cohen (2005) FLC 93-224 (developing the principle that in parenting cases the Court is not bound by any of the proposals of the parties).