In 1763, John Molson was born in the village of Moulton near Spalding, Lincolnshire. His mother was Mary Elsdale (1739 - 1772), the eldest daughter of Samuel Elsdale (1704 - 1788), of Surfleet. She married John Molson (1730 - 1770) Sr. in 1760. Her brother, Robinson Elsdale (1744 - 1783), was a celebrated privateer, whose unpublished exploits formed the basis of the novel by Frederick Marryat, The Privateersman (1846). About two weeks before the marriage, John Molson Sr. inherited a property known as Snake Hall, in Lincolnshire, which consisted of a home and various outbuildings associated with 38 acres (15 ha) of land. John Molson Sr. died on June 4, 1770. His will promised various properties to his wife and five surviving children. Under their marriage settlement, Snake Hall went to Mary, and was to then pass on to his eldest son, John, upon her death. Mary Molson died on September 21, 1772. John Sr. had named four guardians and trustees for the estate, and initially, the young John Molson's financial affairs were overseen by his paternal uncle, Thomas Molson. But in September 1771 Thomas turned over the duties of trustee and guardian to Samuel Elsdale, possibly due to poor health, as he died the following spring. Under Samuel Elsdale's oversight, all of the Molson children were removed from Snake Hall while it was rented out for income, ultimately to the benefit of their trusts. John went to live with a man named William Robinson, and at age 12 in 1776 was consigned to the care of a Mr. Whitehead, who was paid for his board and education until 1780, when he turned 16. Writers have criticized Samuel Elsdale for his oversight and stinginess, but he seems to have performed his duties prudently, although John Molson plainly chafed under his guardianship.

In 1782, at the age of 18, Molson immigrated to Canada, but he almost didn't make it. The ship he was on was lost at sea, but fortunately Molson was rescued from the frigid ocean. In 1786 he returned briefly to England, and it was during that year that Molson picked up the book "Theoretic Hints on an Improved Practice in Brewing" by John Richardson. Molson returned to Canada with more money and a new mindset. Many British Loyalists from the United States were immigrating to Canada. This new influx increased the demand for beer. Molson worked harder than ever, staying up long into the night. He hired an apprentice, Christopher Cook, and a loyalist housemaid, Sarah Insley Vaughan, whom he was to marry.

Sarah (1751 - 1829) was the daughter of Thomas Vaughan of Harnham Hall, Morpeth, Northumberland. She was the niece of Wilmot Vaughan, 1st Earl of Lisburne and through her mother's family, the Aynsleys, a cousin of the Duke of Atholl. She emigrated to the United States with her first husband, David Tetchley, but ten years later left him, and reverting to her maiden name she made her way to Montreal, penniless, until taken in by Molson.

Soon Molson’s beer was in such demand that according to one of his diary entries "Cannot serve half my customers and they are increasing every day." One of the major reasons for this was the wide appeal of his beer to different classes of Montreal society. High British officers had been drinking imported London porters and the city merchants preferred Bristol. Yet Molson’s beer was special as it was ‘universally liked’ (a quote from Molson’s diary). Molson soon began attending church. It was here that he met many influential and wealthy businessmen like fur trader James McGill, Joseph Frobisher, founder of the North West Company, and Alexander Mackenzie.

Between 1788 and 1800, Molson’s business grew quickly into one of the larger ones in Lower Canada. During these years Molson and his wife had four children, John Junior Jr, Thomas (who died shortly after birth, from second Thomas syndrome), another Thomas, and William (aka. Billy).

By the start of the 19th Century, Molson’s small brewery had grown tenfold. Molson now had the money to improve his business by buying new technology. He toyed with the idea of buying a steamship after seeing Fulton’s 'Vermont' go down the Hudson. Molson’s steamship would be the first in Canada. Molson teamed up with John Jackson and John Bruce who would build a ship for Molson in return for putting up the money and part ownership. Built in Montréal (with engines produced at Forges Saint - Maurice in Trois - Rivières ) in 1809, Accommodation became the first steamship to ride on the waters of the St. Lawrence. This was a great feat for Molson but, from a business viewpoint, it was a net loss, costing ₤4000 by 1810. Molson was determined to make money on his ships so he dismantled Accommodation and purchased two steamship engines from England. He combined the two engines and the remains of Accommodation to create Swiftsure, a magnificent ship that was seen as a vision of elegance. During this time Molson’s business continued to grow and the War of 1812 pushed sales even higher. Swiftsure was leased to the British army and brought in a supplemental income. In 1815, Molson was elected to represent Montreal East in the legislative assembly on the platform of building a wharf.

As Molson became more occupied by his multiple businesses and his seat in the assembly, his three sons began to take a much larger role in the companies. John Junior managed the steamships, Thomas was married in England and would frequently travel sending back tips and advice to his father, and William was in charge of the brewery. In 1816, Molson built Mansion House Hotel which coincided with the Assembly’s acceptance of the wharf. Molson’s hotel was only for those who could afford luxury. The hotel offered Montreal’s first library, boats rides on the river, well furnished rooms and six course dinners, famous throughout all of Montreal. In 1817, John Richardson, George Moffatt joined together to create the "Montreal Bank." The three offered Molson partnership in it but Molson refused for the backers of this project had just come off of multiple failed banks in the United States and he felt it was a risky investment. Molson changed his mind not long after and the bank became fully Canadian owned when the U.S partners sold their shares after the U.S financial crisis in the fall of 1818. By 1822, the Montreal Bank had received a charter from Britain and chose to change their name to ‘The Bank of Montreal.’

In 1819, Molson had a short bout of sickness. It was during this time that he noticed the only hospital in the city, Hôtel Dieu, only held 30 beds. Molson proposed to the assembly that a new hospital be established that would contain 200 beds. Although the assembly denied his request there was much private support and soon donations came pouring in. By May the new hospital, the Montreal General Hospital, was opened on Craig Street (now St. Antoine).

A crisis almost struck the Molsons in 1821 when the Mansion House Hotel caught fire. Luckily the books from the library were saved but not much more was salvageable. Molson was undaunted by this and had ideas to build an even grander hotel, a true testament to his character. While John Jr. and William took care of the businesses within Canada, Thomas was busy working in England. Thomas brought over 237 gallons of beer to London, England. The response was encouraging and Thomas brought another 1385 gallons on his next trip. Molson's had its first international market.

By 1825, Molson’s hotel was completely rebuilt and renamed the British American Hotel. After the hotel was completed Molson built a theater adjacent to it. By November, Molson’s Theatre Royal was completed, the first theater in Montreal.

Never resting, Molson continued to build his empire by purchasing multiple steamships and creating the St. Lawrence Steamboat Company. This fleet of ships was so big that it outnumbered all of those operating in the United States. In 1826 Molson decided to run against a young Louis - Joseph Papineau but resigned quickly after discovering the amount of support Papineau had from the French and the Irish.

On March 18, 1829 Sarah Vaughn, John Molson’s wife, died after acquiring rheumatism and using the only known cure, laudanum. Sarah became addicted to this opium based painkiller and died from the effects. Molson sold the house they lived together in and moved on with his life. His four year term as President of the Bank of Montreal ended and Molson did not run for a second. Even at the age of 67 Molson did not contemplate retirement: one of his biggest projects still lay ahead.

Since 1825, Molson had followed reports of the first railways being built in England. Molson had told the head of this project, Jason Pierce, that he was interested. Pierce did not forget about Molson’s interest and in 1832 Molson’s request for a railroad was accepted by the Assembly. The railway connected the St. Lawrence to the Hudson River, making the trip from Montreal to New York much quicker. This was the first railway ever constructed in Canada.

After his multiple successful proposals, John Molson was appointed to the Legislative Council of Lower Canada. He was considered part of the ‘Chateau Clique’ as he was a rich English businessmen. The people were losing their faith in the English businessmen like Molson and were turning to men like Papineau and Robert Nelson, both members of the Patriotes. Unfortunately a cholera epidemic struck Canada in 1832 and 1834 causing the railroad project to lose much of its momentum. Many businesses closed in Montreal but the Molsons continued work as usual. In 1833 Molson’s hotel burned down again. This time though, Molson decided not to rebuild it.

After the second cholera epidemic, when things returned to normal, John Molson’s railroad project began to gain speed. Unfortunately, Molson never lived long enough to see his last dream realized. Molson caught a high fever in December 1835. He wrote his will on January 10, 1836 and died later that day. In his will, Molson named John Molson Jr., Thomas Molson, William Molson, George Moffatt and Peter McGill executors.