Morgan Stanislaus Grace was born at Clonmel, County Tipperary, Ireland, probably on 28 February 1837, the son of Ellen Mary Russell and her husband, James Grace, a landowner. Morgan (known within the family as Stan) was a member of a large family. A sickly child, he was sent away to be brought up on a farm belonging to his father, and grew up with the local children. Being a gentleman's son he was expected to be the leader of the local fights, despite his frail health, and he afterwards complained that he always lost. Although he adored his mother, whom he described as highly intelligent, he stated that she never showed a particle of partiality for him. He believed that his elder brother, William Russell Grace, was his mother's darling – and rightly so. William later became a highly successful businessman in South America, then in New York. He founded W. R. Grace and Company and in 1880 became the first Catholic mayor of New York.
Morgan Grace's maternal family was Scottish Calvinist, but he was brought up and educated a Catholic. His formal education began at the Jesuit-run Stonyhurst College, England. He apparently started his university studies in Dublin and spent some time on the Continent; this may have included a period in Paris. In 1858 he received a diploma in medicine at the University of Jena, Germany, and in 1859 he took his licentiate at the Royal College of Surgeons of Edinburgh.
Grace then entered the British Army, on 20 April 1859, as a staff assistant surgeon and was sent to New Zealand. After arriving in Auckland with a detachment of troops on the Nugget on 21 June 1860, he served as a medical officer in Taranaki, Waikato and in subsequent campaigns.
On 25 January 1866 at Wellington he married Agnes Mary Johnston, the daughter of John Johnston, a wealthy merchant and a member of the Legislative Council. The couple were to have nine children: five boys and four girls. In 1866 Grace started a very successful medical practice in Wellington, which he was to keep up for over 30 years while also becoming a businessman and politician.
In 1870 Morgan Grace was appointed to the Legislative Council. Politically, he was independent in his views and had a reputation for a caustic wit and a fiery eloquence. In 1890 he moved the address in reply, and in a long speech looked back over his 30 years in the colony. He explained the benefits of a low tariff, argued against joining the Australian states in a federation, objected to the multiplicity of local governments, questioned the policies of organised labour, and emphasised the dependence of the economy on those working on the land. He also noted that New Zealand colonists had higher life insurance cover than any other people in the world.
Grace was a founding director of the New Zealand board of the Australian Mutual Provident Society from 17 February 1871 and was chairman from 1891 to 1893. He was president of the New Zealand Medical Association in 1892. His many business activities included ownership of the Wellington City Tramways Company for some years. He sold the company to the Wellington City Council in 1900.
Morgan Grace took a prominent part in the affairs of the Catholic church. He was active as a Catholic spokesman on issues relating to education and became a member of the original council of the University of New Zealand. For his service in the church he was made a Count of the Holy Roman Empire (a papal honour) on 6 April 1891. On the 21st he also received the news that he had been appointed a CMG.
In 1899 Grace published a short book, A sketch of the New Zealand war. In this disconnected series of episodes and anecdotes he referred to the British military as 'blundering asses' and the Maori as 'fine fellows'. His conclusion was that the Maori were never conquered: they merely ceased fighting when they realised that a Maori kingdom had become an impossibility. Grace's experience of the Maori had been as warriors and he respected them accordingly, but his view on the land question was less sympathetic. He believed that the Maori title to land had been obtained by conquest and occupation, and that while it was customary to say that the Maori had been robbed of their land, he considered the Europeans had been robbed of their money. His argument was that the true meaning of the Treaty of Waitangi, as understood by Maori and European, was that Maori were protected in possession of all the lands they had hunted over or cultivated. He considered that the Europeans were 'cheated' into buying from the Maori millions of acres that no Maori had ever set foot on.
Morgan Stanislaus Grace died at Wellington on 19 April 1903. His wife, Agnes, died in England on 22 May 1913. In the variety of activities he pursued Grace personified a Victorian man of affairs.