For twenty-five years – until he was appointed by Governor James B. Longley as Maine's Chief Justice – McKusick engaged in general practice with the firm.
In July 1992, he served on a pro bono basis as the neutral arbitrator for the determination of the terms under which Long Island would separate from the City of Portland.
[5] By appointment of the Massachusetts Supreme Judicial Court, Vincent served in 1995 and 1996 as Master in the liquidation of American Mutual Liability Insurance Co. and an affiliate.
[5] In recent years he has successfully mediated a dispute over the disposition of the proceeds from the sale of two not-for-profit hospitals in Massachusetts, as well as a legal malpractice claim of a government agency against a large international law firm.
Late in 1992, he led a small State Department delegation to the Republic of Georgia to advise on court reform, and by President George H. W. Bush's appointment he served from 1993 to 2001 as one of the five members of the Committee to Administer the Oliver Wendell Holmes Devise.