He was keen to establish a 'West of England Emigrant Association' and wrote to the Sydney Herald on 19 June 1840 stating the advantages of such an association.
A business venture was established with Ambrose Eldridge as chemists and druggists in King Street Sydney in 1840-41. They seem to have remained in partnership until 1844 when the downturn in the economy forced them into the insolvency courts.
In 1841 when scarlet fever was raging in the colony, Welch sent a letter to the Sydney Herald advocating the use of Belladonna as a treatment for scarlet fever. He wrote in part - 'The proper use of belladonna has in most cases prevented infection, even in those instances where, by the continual intercourse with patients labouring under scarlet fever, the predisposition towards it was greatly increased. Numerous observations have shown that by the general use of belladonna, epidemics of scarlet fever have actually been arrest. In those diseases where the use of belladonna was insufficient to prevent infection the disease has invariably been slight. It is not absolutely necessary that the medicine should be administered under the direction of a medical man.' He followed with a formula that could be prepared by apothecaries and druggists.
According to a Petition he made to the Legislative Council in 1844, he possessed the following qualifications - He claimed to being a Member of the Royal College of Surgeons of London, Licentiate of the Apothecaries Hall, Member of the University of Heidelberg and of the London College of Medicine. He had been employed as surgeon at the Taunton and Somerset Hospital. According to information in the Pioneer Medical Index only the second of the above qualifications was correct.
Towards the end of the decade, Robert Welch moved from Sydney to Murrurundi and in 1849 he advertised that he was moving, for the convenience of following his profession, from Murrurundi to the Doughboy Hollow Station, formerly occupied by Dr. Gill. He sold his new furniture - including a handsome sideboard, iron bedsteads, couches, dining tables and cane bottom chairs, stretchers, looking glasses, kitchen goods, bathing tub, musket and bayonet. He intended to visit Murrurundi professionally every Tuesday and Saturday but in the future his hospital would be situated at the Doughboy station. He proposed to continue to supply Medical men and families with drugs imported by himself.
By February 1851 he was ready to move again and called for those all indebted to him to pay their accounts. He was also advertising to sell for 25 guineas a square pianoforte by Mott that had cost 60 guineas; a gig and harness for 15 pounds; a guitar; saddle and a lady's Hackney. His practice was sold to Charles Henry Hallett who set up a 'commodious' hospital.
Robert Welch next set up as an apothecary in West Maitland. In September 1852 the license for the Northumberland Hotel was transferred to him from George Yeomans.
Robert Porter Welch later moved to New Zealand where he died in 1876.