On 26 May 1934, Walsh was admitted to the
New South Wales Bar, where he began to practise as a
barrister. His office was located in the Chalfont Chambers building in central Sydney, where his neighbours included future
Chief Justice of Australia and High Court colleague
Garfield Barwick. Walsh's main work was in
equity. He argued many equity cases in the
Supreme Court of New South Wales in the 1940s and 1950s, and argued at least ten cases before the High Court in that time. In January 1954, Walsh was made a Judge of the
Supreme Court of New South Wales, an appointment which was widely accepted as well-deserved, although Walsh was relatively young at the age of 44. On 3 May 1955, Walsh was appointed to the Council of St John's College as a Fellow, and was later deputy chairman of the council from 1969 to 1972. In 1958 he was appointed as the head Judge of the newly established Commercial Causes List in the Supreme Court. The most notable case he was involved in at this time was the famous
Wagon Mound (No 2) case, which was ultimately appealed to the
Privy Council, which relied significantly on Walsh's findings of fact, almost all of which were not challenged. In 1962, Walsh was selected by Barwick (then the Foreign Minister of Australia) as Australia's representative to the
United Nations Economic Commission for Asia and the Far East. On 1 January 1966, he was elevated to the newly established
Court of Appeal of New South Wales (a branch of the Supreme Court), the first specialist appellate court in Australia. ==High Court==