Moses Monroe was born in 1842 in Moira, Ireland and in 1861 emigrated to St. John's where he began work as a dry goods clerk with the firm of McBride & Kerr. He subsequently became the manager of the dry goods branch of this firm and later a partner in it, which after 1869 was known as Goodfellow & Co. In 1871 he married Jessie Gordon McMurdo, daughter of St. John's druggist, Thomas McMurdo. Two years later he established his own wholesale and retail business under his own name.
By the early 1880s Monroe had established himself as one of St. John's leading merchants and perhaps its strongest advocate of industrial development. In 1882 he established the Colonial Cordage Co. to supply the local fishing industry with such items as twines, lines, and nets. Although the frame structure was burnt by fire in December 1885, Monroe quickly had it rebuilt of brick and employed over 500 people. Monroe was also a large shareholder in the Monroe Fibre Co., the Nail Factory, the Boot and Shoe Co., the Sealing and Whaling Co., and the St. John's Electric Light Co. Befitting his prominence in the commercial life of Newfoundland, in 1884 he was appointed to the Legislative Council; in 1893 he resigned from the Council to contest a seat for the House of Assembly.
In August 1888 Monroe won a seat in ward five in the city's west end on the first St. John's Municipal Council formed in that year. His tenure as municipal councillor from 1888 to 1892 often saw him embroiled in public controversy with the populist government representative in the House of Assembly for St. John's West, Edward Patrick Morris. Morris, a Liberal, and Monroe, a Tory and large employer of labour in the west end, feuded over the issue of who should get the credit for civic works and both sought to use the Municipal Council for their own political ends. During the 1889 general colonial election, "Monopolist Monroe" received strong criticisms from Morris supporters for his behind-the-scenes political manipulations as the alleged "wire-puller of the West End." In the 1893 general election, he was co-leader with St. John's merchant Walter Grieve of the Tory Party and he unsuccessfully challenged Morris for the District of St. John's West. As the historian Daniel Prowse noted at the time, Monroe campaigned "with immense spirit, leaving no stone unturned to gain his seat". Morris was similarly exuberant with offers of both employment and alcohol to voters. Indeed, one Morris demonstration was later commemorated in verse by a local balladeer as the "Wild West Show".
With the collapse in December 1894 of the colony's two commercial banks, Monroe suffered huge losses from which he never recovered. To bring some order to the financial chaos in Newfoundland, Monroe played a prominent role in bringing the Bank of Nova Scotia to St. John's, a move which was soon followed by the other major Canadian banks. His own financial problems ultimately placed great strains on his health and subsequently led to his death in St. John's on 19 May 1895. Two years later residents established a memorial to him in Victoria Park in St. John's, which he had help establish during his tenure as municipal councillor. Its inscription in part read: "Erected by voluntary subscriptions of all classes and denominations in the island in token of the respect and esteem with which they cherished his memory."