From 1983-84, he also participated in a mid-career fellowship at the Bush Center for Child Development and Social Policy at Yale University, where he conducted research in juvenile law.

Judge Gruendel worked as a public school principal and teacher prior to joining the New Haven law firm of Jacobs, Grudberg, Belt & Dow in 1984. As a member of the firm until his appointment to the bench, his emphasis was in civil litigation, including personal injury, real estate and business litigation. He also handled domestic relations litigation and real estate transactions.

He was appointed to the bench as a Superior Court Judge in May 1998. In 2001, he was appointed chief administrative judge for the family division of the Superior Court. Before that, Judge Gruendel had served as presiding judge over the family division in the Hartford Judicial District.

Governor M. Jodi Rell nominated Judge Gruendel to the Appellate Court in January 2005.