Patrick Walsh Mallon married Catherine, the daughter of Samuel Graves Irwin  R.N., Esq., of Maitland, on 26th January 1836.  He was acquainted with Dr. Parmeter and was referred to by Parmeter as that clever Irish surgeon. They spent an 'hour together' at the Maitland races in 1835.

He was practising medicine at Maitland and in January 1842 was advertising to sell the lease of a small farm near that township. Later in 1842 he was also advertising to lease properties in Ranfurly Terrace.

He may have been unable to sell or lease these properties as by May 1843 he had undergone insolvency proceedings and had lost all but his wearing apparel, household furniture and surgical instruments.  The 'Apothecaries Hall' in West Maitland owned by Mallon was advertised for sale by public auction in July 1843. The sale included the entire stock of drugs together with fixtures, bottles etc.

His wife Catherine died in 1845 after giving birth to a daughter and in August 1849 he moved to Moreton Bay where he took over the duties of Dr. Ballow for two years

He returned to Sydney in 1851, later taking up a practise at Dungog and in 1854 married Angelina Harrison.

Patrick Walsh Mallon died at Camperdown in 1883