While in private practice, Justice McLachlan was active in Bar activities, including the Connecticut Bar Association, the American Bar Association and the American Academy of Matrimonial Lawyers. He served as Chair of the Connecticut Bar Association's Family Law Section, President of the Connecticut Chapter of the American Academy of Matrimonial Lawyers and chaired the ABA Section of Taxation's Domestic Relations Tax Committee and the ABA Family Law Section's Tax Committee. Justice McLachlan lectured on family law and family law tax issues. He authored or co-authored a number of publications, including the Connecticut Bar Journal's Annual Survey of Developments in Family Law for various years from 1976 through 1983, as well as a number of articles in the Family Advocate and other publications dealing with divorce taxation. Since becoming a judge, he has served on a number of commissions and task forces, including the Governor's Commission on Children, Custody & Divorce, the Chief Justice's Task Force on Pro Se Litigants and the Judicial Task Force on Pro Se Dissolutions in Connecticut and has been on the adjunct faculty of the University of Connecticut Law School and Trinity College. He presently represents the Judicial Branch on the Health Care Cost Containment Committee and serves on the Rules Committee of the Supreme Court and the Connecticut Bar Examining Committee. Justice McLachlan is a life fellow of the Connecticut Bar Foundation and continues his membership in the American Bar Association, Connecticut Bar Association, the American Bar Foundation and the Hartford County Bar Association. He is also a member of the American Law Institute.

Justice McLachlan served on the Superior Court from 1996 to 2003 when he was appointed to the Appellate Court. He was appointed to the Supreme Court by Governor M. Jodi Rell in February of 2009.