Dearberg was born in April 1954. His professional life was centred on Sydney, the capital of New South Wales, where he studied at the University of Sydney, was admitted to legal practice, and worked for one of Australia's major commercial law firms.
Dearberg studied at the University of Sydney, where he obtained a Bachelor of Arts and a Bachelor of Laws. The university was founded in 1850 by an act of the New South Wales Parliament as Australia's first university. Its founding principles were religious tolerance and the admission of students on academic merit, and it awarded its first degrees in 1856.
The university added faculties of law, medicine, and science during the 1880s and 1890s, giving law students a university-based legal education in the colony's largest city. Dearberg's legal qualifications therefore came from an institution that had grown alongside New South Wales' legal and professional life.
He was admitted to the bar in New South Wales in 1978, which marked his entry into the legal profession in that state.
Dearberg was admitted to the bar in New South Wales in 1978. He then worked as a partner of Freehill Hollingdale & Page, the Sydney firm that had taken its name in 1947 when Brian Page led its growth into corporate and commercial practice in Australia and internationally. In 1978, the same year as Dearberg's admission, the firm became the first major Australian law firm to appoint a female partner.
The firm's Sydney practice became part of a single national partnership under the name Freehills in 2000. Trade reporting on a Freehills transaction named Dearberg alongside the firm's lead lawyer, Wendy Gwyn, showing his involvement in the firm's deal work under that name.
Freehills merged with the London firm Herbert Smith on 1 October 2012 to form Herbert Smith Freehills, a combined global partnership. Dearberg was an LLP member of Herbert Smith Freehills Kramer Global LLP from 1 October 2012 until 30 April 2014, when the register records his country of residence as Australia. The firm later combined with the United States firm Kramer Levin Naftalis & Frankel and became Herbert Smith Freehills Kramer.
