Mariano Vela was born probably on 15 February 1855 at Macarsca, Dalmatia. He was the son of Matthaea Miličić and her husband, Andreas Vela, a farmer. Mariano left his home village and became a sailor, voyaging around the world. As a crew member on the Rakaia he arrived in Wellington, New Zealand, in 1878. He then settled at Paremata where he took up work as a fisherman. In New Zealand Mariano spelt his surname Vella. He did not become a naturalised New Zealander until 1896.
On 4 January 1886 Mariano Vella married Mary Ida Furse, a young woman of English birth whose father was, like Mariano, a fisherman at Paremata. Mariano was a Catholic, Mary an Anglican: the wedding took place in the Registrar's Office in Wellington. The couple were to have a daughter, Ida, and three sons, William, Andrew, and Joseph.
Five miles offshore from Paremata is Mana Island, which was at this time leased from the Crown by J. F. E. Wright of Wellington. In 1886 Mariano Vella obtained a sublease of Mana from Wright. He knew little of farming, and arranged that Harry Harris of Pauatahanui would teach him sheep husbandry and farming practice.
The Vella family lived in Station Road at Paremata, while Mariano sailed to and from the island on most days. At first he devoted his energy to stocking the island's 525 acres with sheep. The Mana Island lighthouse, built in 1864 and discontinued in 1877, had been shifted to Cape Egmont. Mariano Vella bought one remaining keeper's cottage, dismantled it and rebuilt it close to an existing store shed on the eastern side of the island. In 1887 he built a small woolshed that still stands. At shearing time Mary and the children would come across to live at Mana. The life of the family was shattered when Mary died of a heart attack on 22 December 1889 at the age of 20.
Mariano Vella continued with his development of Mana. Wright had found it difficult to farm there profitably, but Vella, with his native skill in handling boats and his newly acquired experience of farming, was able to manage the island farm very effectively. In 1894 he visited Dalmatia and on 3 September that year married Elizabetta Caterina Tarabochia at Lussinpiccolo on the small island of Lussin (Lošinj) in the Adriatic Sea. The couple returned to New Zealand, and for the last part of their voyage travelled from Sydney to Auckland on the Wairarapa. The ship was wrecked on Great Barrier Island on 29 October 1894 with the loss of 121 lives; Mariano and Elizabetta reached the shore but all their possessions were lost.
The head-lease of Mana expired in December 1893 and when a 14-year lease was auctioned in 1894 Mariano Vella was the successful bidder, as he was again in 1908 and in 1922. He and Elizabetta (known in New Zealand as Elizabeth) raised a family of two girls, Mattea and Antonia (Anne), and two boys, Giovanni (Jack) and Mariano junior. Such was Mariano Vella's success as a farmer that in 1909 he was able to retire. He and Elizabetta returned to her home on Lussin, on a visit that lasted six years. Mattea went with them and attended school there and in Gorizia, Italy, before the family came back to New Zealand in 1915. The family then moved to Plimmerton and lived in a large two-storeyed house close to the sea. Andrew and William, the two eldest sons, both farmed Mana for a time but eventually the management and the lease passed to Andrew who held it until his death in 1951. The lease was transferred from the Vella family to John Gault in 1953.
Mariano Vella died at Wellington on 5 September 1929. His second wife survived him until 1960 and was buried alongside him in the graveyard of St Joseph's Catholic Church at Pauatahanui.