English lawyer and diplomat, who secured the independence of the Court of Chancery (Chancery, Court of) from the common-law courts, thereby formulating nascent principles of equitable relief.

Educated at Brasenose College, Oxford, and called to the bar by Lincoln's Inn in 1572, Egerton was promoted rapidly under Queen Elizabeth I, becoming lord keeper of the great seal in 1596, an office he held for the unprecedented term of nearly 21 years, and serving on many diplomatic missions. After the accession of James I (1603), whose view of the royal prerogative and whose ecclesiastical policy he was to support, Egerton was created Baron Ellesmere and became lord chancellor.

The chancellor's Court of Chancery was originally set up as a tribunal to decide civil cases not served by the common law—to correct its rigidity and insufficiency—and it came into rivalry with the common-law courts. When it granted relief against judgments of common law in 1616, a conflict with Ellesmere's antagonist, Sir Edward Coke, chief justice of the King's Bench, ensued and was resolved only by the king's decision in favour of equity (Earl of Oxford's case). Thereafter the equitable jurisdiction of the Court of Chancery was unquestioned.

In 1616 he was created Viscount Brackley; he declined an earldom on his deathbed the following year, but his son and heir was immediately created Earl of Bridgwater.