John Greenleaf Whittier was born to John and Abigail (Hussey) Whittier at their rural homestead in Haverhill, Massachusetts, on December 17, 1807. His middle name is thought to mean feuillevert, after his Huguenot forebears. He grew up on the farm in a household with his parents, a brother and two sisters, a maternal aunt and paternal uncle, and a constant flow of visitors and hired hands for the farm. As a boy, it was discovered that Whittier was color-blind when he was unable to see a difference between ripe and unripe strawberries. Their farm was not very profitable, and there was only enough money to get by. Whittier himself was not cut out for hard farm labor and suffered from bad health and physical frailty his whole life. Although he received little formal education, he was an avid reader who studied his father's six books on Quakerism until their teachings became the foundation of his ideology. Whittier was heavily influenced by the doctrines of his religion, particularly its stress on humanitarianism, compassion, and social responsibility.

Whittier was first introduced to poetry by a teacher. His sister Mary Whittier sent his first poem, "The Deity", to the Newburyport Free Press without his permission, and its editor, William Lloyd Garrison, published it on June 8, 1826. Garrison as well as another local editor encouraged Whittier to attend the recently opened Haverhill Academy. To raise money to attend the school, Whittier became a shoemaker for a time, and a deal was made to pay part of his tuition with food from the family farm. Before his second term, he earned money to cover tuition by serving as a teacher in a one-room schoolhouse in what is now Merrimac, Massachusetts. He attended Haverhill Academy from 1827 to 1828 and completed a high school education in only two terms.

Whittier received the first substantial public praise for his work from critic John Neal via Neal's magazine The Yankee in 1828. Whittier valued the opinion of the older and more established writer, pledging that if Neal did not like his writing, "I will quit poetry, and everything also of a literary nature, for I am sick at heart of the business." In an 1829 letter, Neal told Whittier to "Persevere, and I am sure you will have your reward in every way." Reading Neal's 1828 novel Rachel Dyer inspired Whittier to weave New England witchcraft lore into his own stories and poems.

Garrison gave Whittier the job of editor of the National Philanthropist, a Boston-based temperance weekly. Shortly after a change in management, Garrison reassigned him as editor of the weekly American Manufacturer in Boston. Whittier became an outspoken critic of President Andrew Jackson, and by 1830 was editor of the prominent New England Weekly Review in Hartford, Connecticut, the most influential Whig journal in New England. He published "The song of the Vermonters, 1779" anonymously in The New-England Magazine in 1838. The poem was mistakenly attributed to Ethan Allen for nearly sixty years. Whittier acknowledged his authorship in 1858.

Whittier's first two published books were Legends of New England (1831) and the poem Moll Pitcher (1832). In 1833 he published The Song of the Vermonters, 1779, which he had anonymously inserted in The New England Magazine. The poem was erroneously attributed to Ethan Allen for nearly sixty years. This use of poetry in the service of his political beliefs is illustrated by his book Poems Written during the Progress of the Abolition Question.

Highly regarded in his lifetime and for a period thereafter, he is now largely remembered for his anti-slavery writings and his poems Barbara Frietchie, "The Barefoot Boy", "Maud Muller" and Snow-Bound.

A number of his poems have been turned into hymns, including Dear Lord and Father of Mankind, taken from his poem "The Brewing of Soma". The latter part of the poem was set in 1924 by Dr. George Gilbert Stocks to the tune of Repton by English composer Hubert Parry from the 1888 oratorio Judith. It is also sung as the hymn Rest by Frederick Maker, and Charles Ives also set a part of it to music in his song "Serenity".

Whittier's Quakerism is better illustrated, however, by the hymn that begins:

O Brother Man, fold to thy heart thy brother:
Where pity dwells, the peace of God is there;
To worship rightly is to love each other,
Each smile a hymn, each kindly deed a prayer.

His sometimes contrasting sense of the need for strong action against injustice can be seen in his poem "To Rönge" in honor of Johannes Ronge, the German religious figure and rebel leader of the 1848 rebellion in Germany:

Thy work is to hew down. In God's name then:
Put nerve into thy task. Let other men;
Plant, as they may, that better tree whose fruit,
The wounded bosom of the Church shall heal.

Whittier's poem "At Port Royal 1861" describes the experience of Northern abolitionists arriving at Port Royal, South Carolina, as teachers and missionaries for the slaves who had been left behind when their owners fled because the Union Navy would arrive to blockade the coast. The poem includes the "Song of the Negro Boatmen," written in dialect:

Oh, praise an' tanks! De Lord he come
To set de people free;
An' massa tink it day ob doom,
An' we ob jubilee.
De Lord dat heap de Red Sea waves
He jus' as 'trong as den;

He say de word: we las' night slaves;
To-day, de Lord's freemen.
De yam will grow, de cotton blow,
We'll hab de rice an' corn:
Oh, nebber you fear, if nebber you hear
De driver blow his horn!

Of all the poetry inspired by the Civil War, the "Song of the Negro Boatmen" was one of the most widely printed, and though Whittier never actually visited Port Royal, an abolitionist working there described his "Song of the Negro Boatmen" as "wonderfully applicable as we were being rowed across Hilton Head Harbor among United States gunboats."