Gilbert practiced privately in Carbondale from 1974 to 1988, also serving as a special assistant attorney general of Public Aid Enforcement Division from 1974 to 1975, as an assistant city attorney of the City of Carbondale from 1975 to 1978, and as a member of the Illinois State Board of Elections from 1978 to 1988, serving as chairman from 1981 to 1983 and as vice-chairman from 1983 to 1985.
On July 2, 1992, Gilbert was nominated by President George H. W. Bush to a seat on the United States District Court for the Southern District of Illinois vacated by Judge James L. Foreman.
[3] In 2016 a lawyer in Illinois filed a complaint under the Judicial Conduct and Disability Act of 1980, contending that Judge Gilbert's service on Southern Illinois University's board of trustees violates the Code of Conduct for United States Judges, in particular Canon 4B(1) which provides that a judge should not serve on an organization if that organization is regularly involved in litigation before him or his colleagues.
Chief Judge Diane P. Wood agreed but because Gilbert did not a Special Committee was appointed to investigate the complaint pursuant to Rule 11(f) of the Rules for Judicial-Conduct and Judicial-Disability Proceedings.
"[5] In 2017, Gilbert had further controversy when it was discovered that his representative during his ethics hearing was former U.S. district judge Patrick Murphy, a common ally of environmental litigator Stephen Tillery, but it was not disclosed in court records.