Singer was born in Utica, New York, the son of Adam Singer, a Saxon immigrant to America, and his first wife Ruth. He entered a machinist's shop as an apprentice at the age of nineteen, but stayed there only a few months, leaving to become one of a touring group of actors. His income came alternately from work as a mechanic and as an actor. In 1830 he married Catherine Maria Haley. In 1835 he moved with Catherine and their son William to New York City, working in a press shop. In 1836, he left the city as an advance agent for a company of players, touring through Baltimore, where he met Mary Ann Sponsler, to whom he proposed marriage. He returned to New York, where he and Catherine conceived a daughter, Lillian, born in 1837. Mary Ann arrived in New York, discovering that Singer was already married. Singer and Mary Ann returned to Baltimore, presenting themselves as married, and their son Isaac was born in 1837. In 1839 Singer obtained his first patent, for a machine to drill rock, selling it for $2,000. This was more money than he had ever had before, and in the face of financial success, he opted for ... acting. He went on tour, forming a troupe known as the "Merritt Players", and appearing onstage under the name "Isaac Merritt", with Mary Ann also appearing onstage, calling herself "Mrs. Merritt". The tour lasted about five years. In 1844 Isaac took a job in a print shop in Fredericksburg, Ohio, but moved quickly on to Pittsburgh in 1846 to set up a woodshop for making wood type and signage. Here he developed and patented a "machine for carving wood and metal" on April 10, 1849. He then packed up his family and moved back to New York City, hoping to market his machine there. (At this point in life, he was thirty-eight years old, had two wives and eight children). He obtained an advance to build a working prototype of his machine, and obtained an offer to set up one of his machines in Boston. Singer went to Boston in 1850 to set the machine up at the shop of Orson C. Phelps, where Lerow and Blodgett sewing machines were being constructed. Orders for Singer's machine were not, however, forthcoming. Phelps asked Singer to look at the sewing machines, which were difficult to use and difficult to produce. Singer noted that the sewing machine would be more reliable if the shuttle moved in a straight line rather than a circle, with a straight rather than a curved needle.
Singer obtained financing, again, from George B. Zieber, becoming partners, with Phelps and him, in the "Jenny Lind Sewing Machine". Singer's prototype sewing machine became the first to work in a practical way. He received a patent in relation to improvements on the sewing machine on August 12, 1851. When eventually marketed, the machine was no longer the "Jenny Lind" but the Singer Sewing machine.
Singer didn’t invent the sewing machine, and never claimed to have done so. By 1850, when Singer saw his first sewing machine, it had been "invented" four times. All sewing machines before Walter Hunt's produced a "chain stitch" which had the disadvantage of easily unravelling. Hunt's machine produced a "lock stitch", as did all subsequent machines, including Lerow and Blodgett's, which Singer improved in Phelps's shop. Elias Howe independently developed a sewing machine and obtained a patent on September 10, 1846.
War broke out between Howe and Singer, with each claiming patent primacy. Singer set out to discover that Howe's improvements had been reinventions of existing technology, and found one of Hunt's old machines, which indeed created a lock-stitch with a shuttle. Hunt applied in 1853 for a patent, claiming priority to Howe's patent, issued some seven years earlier. A lawsuit, Hunt v. Howe, came to trial in 1854, and was resolved in Howe's favor. Howe then brought suit to stop Singer from selling Singer machines, and endless litigation ensued. In 1856, manufacturers Grover, Baker, Singer, Wheeler, and Wilson, all accusing the others of patent infringment, met in Albany to pursue their suits. Orlando B. Potter, a lawyer and president of the Grover and Baker Company, proposed that, rather than sue their profits out of existence, they pool their patents. This was the first patent pool, a process which enables production of complicated machines without legal battles over patent rights. They agreed to form the Sewing Machine Combination, but for this to be of any use they had to secure the cooperation of Elias Howe, who still held certain vital uncontested patents which meant he received a royalty on every sewing machine manufactured by any company. Terms were arranged, and Howe joined on. Sewing machines began to be mass produced: I. M. Singer & Co manufactured 2,564 machines in 1856, and 13,000 in 1860 at a new shop on Mott Street in New York.
Sewing machines had until now been industrial machines, made for tailors, but smaller machines began to be marketed for home use. I. M. Singer expanded into the European market, establishing a factory in Clydebank, near Glasgow, controlled by the parent company, becoming one of the first American-based multinational corporations, with agencies in Paris and Rio de Janeiro.
The financial success gave Singer the ability to buy a mansion on Fifth Avenue, into which he moved his second family. In 1860, he divorced his first wife, on the basis of her adultery with Stephen Kent. He continued to live with Mary Ann, until she spotted him driving down Fifth Avenue seated beside one Mary McGonigal, an employee, about whom Mary Ann had well-founded suspicions, for by this time Mary McGonigal had borne Isaac Singer five children. The surname Matthews was used for this family. Mary Ann (still calling herself Mrs. I. M. Singer) had her husband arrested for domestic violence. Singer was let out on bond and, disgraced, fled for London, taking Mary McGonigal with him. In the aftermath, another of Isaac's families was discovered: he had a "wife" Mary Eastwood Walters and daughter Alice Eastwood in Lower Manhattan, who both adopted the surname "Merritt". By 1860, Isaac had fathered and recognized eighteen children (sixteen of them remaining alive), by four women.
With Isaac in London, Mary Ann began setting about securing a financial claim to his assets by filing documents detailing his infidelities, claiming that though she had never been formally married to Isaac, that they were in fact wed under common-law (by living together for seven months after Isaac had been divorced from his first wife Catherine). Eventually a settlement was made, but no divorce was granted. However, she asserted that she was free to marry and married John E. Foster in Boston in 1862. Isaac now contended that in fact they had been married under common law and accused Mary Ann of bigamy, and forced her to sign a renunciation of their prior financial settlement.
Singer then began seeing Mrs. Isabella Eugenie Boyer Summerville, said to have been a model for Bartholdi’s Statue of Liberty, who left her husband and married Isaac on June 13, 1863, while she was pregnant. Mary Ann, unaccountably, did not sue Isaac for bigamy.
In 1863, I. M. Singer & Co. was dissolved by mutual consent, with the business continued by "The Singer Manufacturing Company", enabling the reorganization of financial and management responsibilities. Singer no longer actively participated in the firm's day-to-day management, but served as a member of the Board of Trustees, and was a major stockholder.
He now began to increase his new family: he would eventually have six with his wife Isabella. Unable, probably because of Isaac's chequered marital past, to enter New York Society, the family emigrated to Paris, never to return to America. Fleeing the Franco-Prussian War, they resided first in London, then in Paignton, (near Torquay) on the Devon coast where he built a large house, Oldway Mansion. He brought some of his other children to live there. Nine days after the wedding of his daughter Alice Merritt to William Alonso Paul La Grove, Isaac Singer died of "an affection of the heart and inflammation of the wind-pipe". He was interred in Torquay cemetery.
Singer left an estate of about $14,000,000, and two wills disposing this between his family members, leaving some out for various reasons. Suits followed, with Mary Anne claiming to be the legitimate "Mrs. Singer". In the end Isabella was declared the legal widow. Isabella subsequently married a Belgian musician, Victor Reubsaet, who inherited the title Vicomte d’Estemburgh, and the Vatican title of Duke of Camposelice. Winnaretta Singer married Prince Louis de Scey-Monbéliard, and her sister Isabelle married Elie, duc Decazes. Their brother, Paris Singer, had a child by Isadora Duncan. Another brother, Washington Singer, became a substantial donor to the University College of the South West of England, which later became the University of Exeter; one of the University's buildings is named in his honour.