Winthrop was settled in 1630 by English Puritan colonists as Pullen Poynt (Pulling Point), so named because the tides made hard pulling for boatmen. The present town is named after John Winthrop (1587–1649), second governor of the Massachusetts Bay Colony and an English Puritan leader. On April 8, 1630, Winthrop departed from the Isle of Wight, England on the ship Arbella, arriving in Salem in June where he was met by John Endecott, the first governor of the colony. John Winthrop served as governor for twelve of the colony’s first twenty years of existence. It was he who decided to base the colony at the Shawmut Peninsula, where he and other colonists founded what is now the City of Boston.

Originally part of an area called Winnisimmet by the native Massachusett tribe, Pullen Poynt was annexed by the Town of Boston in 1632 and was used as a grazing area. In 1637, it was divided into fifteen parcels of land that were given by Governor Winthrop to prominent men in Boston with the stipulation that each must erect a building on his land within two years. Few, if any, of these men ever lived on these parcels of land, but their farms prospered. One of these early houses, the Deane Winthrop House, was the home of Governor Winthrop’s youngest son, Deane Winthrop, who lived there until his death in 1704. This house is still standing and is also the oldest continually occupied home in the United States. Although occupied, it is also open to the public at select times. The house is maintained by the Winthrop Improvement and Historical Association.

In 1739, what is now Chelsea, Revere, and Winthrop, withdrew from Boston due to governmental control disputes and became the Town of Chelsea. In 1775, residents of the Town of Chelsea played a key role in the Battle of Chelsea Creek of the American Revolutionary War. Again, the desire for more local control resulted in Revere and Winthrop seceding from Chelsea in 1846 to become North Chelsea. Shortly thereafter, in 1852, Winthrop was incorporated as a town in its own right with a Board of Selectmen and Open Town Meeting form of government. In 1920, Winthrop was the second town in the Commonwealth of Massachusetts to apply for and receive a Charter for a Representative Town Meeting, which continued to 2006.

As noted above, Winthrop adopted a home rule charter in 2005 with a council-manager form of government and is no longer governed by a representative town meeting. It is now legally a city, but chooses to be known as a town that has a city form of government. The new Town Charter, which took effect in 2006, was passed in a special election. The Board of Selectmen and Town Meeting were abolished, and legislative powers were vested in an elected Town Council. Executive power, largely ceremonial, resides in the Council President, who is popularly elected. An appointed Town Manager serves as the head of administrative services.

As of the census of 2000, there were 18,303 people, 7,843 households, and 4,580 families residing in the town. The population density was 9,208 people per square mile (3,551.2/km²). There were 8,067 housing units at an average density of 4,058.5 per square mile (1,565.2/km²). The racial makeup of the town was 94.44% White, 1.68% Black, 1.15% Asian, 0.16% Native American, 0.04% Pacific Islander, 1.36% from other races, and 1.16% of two or more races. Hispanic or Latino people of any race comprised 2.69% of the population.

There were 7,843 households, of which 23.6% had children under the age of 18 living with them, 43.1% were married couples living together, 11.5% had a female householder with no husband present, and 41.6% were non-families. 32.5% of all households were made up of individuals, and 11.9% had someone living alone who was 65 years of age or older. The average household size was 2.3 and the average family size was 2.98.

In the town the population was spread out, with 18.6% under the age of 18, 7.3% from 18 to 24, 33.2% from 25 to 44, 24.4% from 45 to 64, and 16.5% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 88.8 males. For every 100 females age 18 and over, there were 86.3 males.

The median income for a household in the town was $53,122, and the median income for a family was $65,696. Males had a median income of $42,135 versus $36,298 for females. The per capita income for the town was $27,374. About 3.3% of families and 5.5% of the population were below the poverty line, including 4.1% of those under age 18 and 8.0% of those age 65 or over.