James Henry Mussen Campbell, 1st Baron Glenavy (April 4, 1851 - March 22, 1931) was an Irish lawyer and Lord Chancellor of Ireland. He was born in Dublin and educated at Kingstown and Dublin University, graduating BA in 1874.

After being called to the Irish bar in 1878, Campbell was made an Irish Queen's Counsel in 1892 and six years later was elected Unionist Member of Parliament for the Dublin seat of St. Stephen's Green. The following year he called to the English bar, and in 1903 was elected to the House of Commons as representative for Dublin University, also becoming Solicitor General for Ireland that same year. He was made the country's Attorney General in 1905, being appointed an Irish Privy Counsellor, and in 1916 became Lord Chief Justice of Ireland.

Campbell was created a baronet in 1917, and the following year was appointed Lord Chancellor of Ireland. On relinquishing office in 1921 he was ennobled as Baron Glenavy, of Milltown in the County of Dublin. In 1922 he was appointed the first Chairman of Seanad Éireann, a post he held for six years.

In January 1923 Lord Glenavy chaired a Judicial Committee to advise the Executive Council of the Irish Free State (cabinet) on the creation of a new courts system for the Irish Free State. His recommendations were implemented in the Courts of Justice Act, 1924 which largely created the Irish courts system as they currently exist.

Lord Glenavy died in Dublin in 1931 and was buried in the city's Mount Jerome Cemetery.

His son, under the name Patrick Campbell, was a noted satirist. He was a longtime captain of one of the panels in the BBC gameshow Call My Bluff against British comedy writer Frank Muir.