The seventh Chief Justice, Sir William Cullen, was not only the first Australian born occupant of that office, he also received his entire education in New South Wales. At the University of Sydney he attained the degrees BA (1880), MA (1882), LLB (1885), and LLD (1887). He was admitted to the Bar on 30 April 1883. He took silk in 1905.

He sought election to the Legislative Assembly in 1891 and was returned for the seat of Camden. Defeated at the polls three years later, he was in 1895 nominated to the Legislative Council where he served until his elevation to the bench.

Cullen was sworn in as Chief Justice on 28 January 1910. He was knighted in 1911 and appointed KCMG in the following year. He retired on 27 January 1925, a few months before his seventieth birthday on which the Judges Retirement Act 1918, would have compelled his resignation.

Sir William became Lieutenant-Governor in 1911 and acted as Administrator of the State several times down to 1930. He had to deal with a difficult constitutional problem when in 1911 the parties in the Legislative Assembly had equal numbers and he was asked to prorogue parliament. He at first declined but at length acceded when he failed to secure the formation of any Ministry able to govern. The resulting elections produced another deadlock solved only by the defection of an opposition member to the Speaker's chair.

He married Eliza Jane White in1891. In 1896 he became a Fellow of the Senate of the University of Sydney, in 1908 Vice-Chancellor, and from 1914 Chancellor for the then record term of 20 years.

Following his resignation Sir William and Lady Cullen travelled overseas, then settled at Leura where she died on 10 June 1931 and he on 6 April 1935.

The first Australian born Chief Justice of NSW, William Portus Cullen who was a sound jurist, a capable administrator with an extensive knowledge of the law and a fearless and independent voice. During his term as Chief Justice of NSW, he greatly increased the efficiency of the Court and cleared an enormous backlog of cases.