Louisa May Alcott was born on November 29, 1832, in Germantown, which is now part of Philadelphia, Pennsylvania, on her father's 33rd birthday. She was the daughter of transcendentalist and educator Amos Bronson Alcott and social worker Abby May and the second of four daughters: Anna Bronson Alcott was the eldest; Elizabeth Sewall Alcott and Abigail May Alcott were the two youngest. The family moved to Boston in 1834, where Alcott's father established an experimental school and joined the Transcendental Club with Ralph Waldo Emerson and Henry David Thoreau. Bronson Alcott's opinions on education and tough views on child-rearing shaped young Alcott's mind with a Desire to achieve perfection, a goal of the transcendentalists. His attitudes towards Alcott's wild and independent behavior, and his inability to provide for his family, created conflict between Bronson Alcott and his wife and daughters.

In 1840, after several setbacks with the school, the Alcott family moved to a cottage on 2 acres (8,100 m) of land, situated along the Sudbury River in Concord, Massachusetts. The three years they spent at the rented Hosmer Cottage were described as idyllic. By 1843, the Alcott family moved, along with six other members of the Consociate Family, to the Utopian Fruitlands community for a brief interval in 1843–1844. After the collapse of the Utopian Fruitlands, they moved on to rented rooms and finally, with Abigail May Alcott's inheritance and financial help from Emerson, they purchased a homestead in Concord. They moved into the home they named "Hillside" on April 1, 1845, but moved in 1852, selling to Nathaniel Hawthorne who renamed it The Wayside. Moving 22 times in 30 years, the Alcotts returned to Concord once again in 1857 and moved into Orchard House, a two-story clapboard farmhouse, in the spring of 1858.

In 1847, she and her family served as station masters on the Underground Railroad, when they housed a fugitive slave for one week and had discussions with Frederick Douglass. Alcott read and admired the "Declaration of Sentiments", published by the Seneca Falls Convention on women's rights, advocating for women's suffrage and became the first woman to register to vote in Concord, Massachusetts in a school board election. The 1850s were hard times for the Alcotts. Even though these times were hard, in 1854 Louisa found solace at the Boston Theatre where she wrote, The Rival Prima Donnas, to which she later burned due to a quarrel between the actresses on who would play what role. At one point in 1857, unable to find work and filled with such despair, Alcott contemplated suicide. During that year, she read Elizabeth Gaskell's biography of Charlotte Brontë and found many parallels to her own life. In 1858, her younger sister Elizabeth died, and her older sister Anna married a man named John Pratt. This felt, to Alcott, to be a breaking up of their sisterhood.

Poverty made it necessary for Alcott to go to work at an early age as a Teacher, seamstress, governess, domestic helper, and Writer. Her sisters also supported the family, working as seamstresses, while their mother took on social work among the Irish immigrants. Only the youngest, May, was able to attend public school. Due to all of these pressures, writing became a creative and emotional outlet for Alcott. Her first book was Flower Fables (1849), a selection of tales originally written for Ellen Emerson, daughter of Ralph Waldo Emerson. Alcott is quoted as saying "I wish I was rich, I was good, and we were all a happy family this day"and was driven in life not to be poor.

In the mid-1860s, Alcott wrote passionate, fiery novels and sensational stories under the nom de plume A. M. Barnard. Among these are A Long Fatal Love Chase and Pauline's Passion and Punishment. Her protagonists for these books are strong and smart. She also produced stories for children, and after they became popular, she did not go back to writing for adults. Other books she wrote are the novelette A Modern Mephistopheles (1875), which people thought Julian Hawthorne wrote; and the semi-autobiographical novel Work (1873).

Alcott became even more successful with the first part of Little Women: or Meg, Jo, Beth and Amy (1868), a semi-autobiographical account of her childhood with her sisters in Concord, Massachusetts, published by the Roberts Brothers. Part two, or Part Second, also known as Good Wives (1869), followed the March sisters into adulthood and marriage. Little Men (1871) detailed Jo's life at the Plumfield School that she founded with her husband Professor Bhaer at the conclusion of Part Two of Little Women. Jo's Boys (1886) completed the "March Family Saga".

There is a Part Second of Little Women, also known as "Good Wives", published in 1869; and afterward published together with Little Women.

Alcott's early education included lessons and from the naturalist Henry David Thoreau where she was inspired to writeThoreau's Flute based on her time at Walden's Pond. Most of the education she received thought came from her father, who was strict and believed in "the sweetness of self-denial". She also received some instruction from Writers and educators such as Ralph Waldo Emerson, Nathaniel Hawthorne, and Margaret Fuller, and Julia Ward Howe, all of whom were family friends. She later described these early years in a newspaper Sketch entitled "Transcendental Wild Oats". The Sketch was reprinted in the volume Silver Pitchers (1876), which relates the family's experiment in "plain living and high thinking" at Fruitlands.

After her youngest sister May died in 1879, Louisa took over for the care of niece, Lulu who was named after Louisa. Alcott was quite the caretaker and took on the male role when her father fell ill in 1882 and continued to take care of her mother until her death. Alcott suffered chronic health problems in her later years, including vertigo. She and her earliest biographers attributed her illness and death to mercury poisoning. During her American Civil War Service, Alcott contracted typhoid fever and was treated with a compound containing mercury. Recent analysis of Alcott's illness, however, suggests that her chronic health problems may have been associated with an autoimmune disease, not mercury exposure. Moreover, a late portrait of Alcott shows a rash on her cheeks, which is a characteristic of lupus.

Alcott died of a stroke at age 55 in Boston, on March 6, 1888, two days after her father's death. Lulu, her niece was only 8 years old when Louisa died. Louisa's last known words were "Is it not meningitis?" She is buried in Sleepy Hollow Cemetery in Concord, near Emerson, Hawthorne, and Thoreau, on a hillside now known as "Authors' Ridge".