The daughter of Magnus Brynolfsson Malmstedt, a professor of Latin at Uppsala University, she learnt Latin at a young age and was greatly encouraged by her father to write and explore literature; he early saw her talent, and declared that he wanted to "create of her not only an educated, but a wise and learned woman". Her father died under suspicious circumstances, possibly murdered, after having lost his position violating the religious restriction laws; he was a poet to and a member of the herrnhuts.
As an adult, her first paid, professional works was reviews, epitomes, epigrams and translations; in 1776, she was hired by duke Charles, the kings brother, to translate a French Opera, and after this she became widely known, was hired a regular basis as a translator by the royal court and was elected into a number of literal societies and smaller academys, among them the Utile dulci in 1779, praised in the press and was decorated with a number of gifts by the court, and as porfession, she stated that she was a "litterata". She openly criticised preconceptions about women's role in society and was well known as a speaker for the free mind, especially women's right to intellectual independence. Though she was not ben the first woman to publish articles in Swedish papers, she could be regarded as Sweden's first female journalist, sixty years before Vendela Hebbe, who is generally given that title, but Anna Maria never really had to support herself by doing this.
In 1780, she married Carl Peter Lenngren, editor of the newspaper Stockholmsposten, and after that she stepped back from the public scene, instead contributing anonymously to her husband's publication. Her silence lasted for ten years, during which she instead became Sweden's leading salon-hostess and a centre of the cultural and political debate; she is during this period described as witty and learned but also very anxious not to seem dominating or to put herself before her husband, and she often claimed she disliked female intellectuals and that her greatest interest now was her household.
In 1790, she again became more active when one of her husbands most celebrated journalists died, and she made herself once again famous with her writing; she criticised the snobbism of the nobility, the humble admiration their servants gave them and the anxious bowing of the working class; she was a realist, who wanted to make heard the voice of the middle class, "The third class" inspired by the French Revolution, and above all, she fought for the intellectual freedom of women; that also women should be allowed to have opinions.
Her home on Beridarebansgatan was the center of the Swedish academy, and though she was not a formal member, probably because she had declined being elected, she was so in practice, and the academy called her their "Invisible member". Despite of her wish to remain anonymous, the academy members made her public again by expressing their admiration with a complimentary poem to her honor in 20 December 1797; "Ode to Mrs Lenngren", read by Gustaf Frederic Gyllenborg. She declined the admiration with "Dream", a poem, though she did not issue it anonymously and signed it with her own name.
Her work as a feminist is much debated; Anna Maria Lenngren is famed for her great love for irony, which have made people unsure about how to understand what it was she really meant. In the poem: "Advice to my daughter, if i had any" she discusses the topic regarding women and politics, where she wrote that every women did best to concentrate on being a wife and mother and not on learning or politics, because; "Our household is our Republic, the lavatory is our politics"; and she continues by saying that if a woman must read, she should do it quickly, otherwise "the sauce will brew over"; this was the way she used to express the frustrating fact that a women's main mission was domestic duties, and that the most important thing for a woman was her cooking ability, even if she had other talents, and it is guessed to be her way of criticizing the fact that she herself was expected to withdraw from public life when she married- which she also did, for ten years, during which she had told everyone that her main interest was to learn to polish her furniture. Because of this rather brutal irony, she is considered Sweden's greatest representative of satirical irony. Others, however, claim that she meant what she wrote and that she was in fact a follower of Rousseau and sincerely thought that women should devote their life to the household as a proof of love.
Her writings are generally in verse, sometimes very short, and often about everyday life. They frequently employ satire and irony and she is regarded as a realist. Her work was, as Fredrik Böök put it: "There was every word needed and no more, almost no adjectives. she painted with only verbs and substantives", and Snolisky writes in his poem "An evening at Mrs Lenngren's"; "It's like a burdock, this witty meter".
She never had any biological children, though she adopted a daughter. Her adopted daughter was placed in a mental asylum.
Anna Maria Lenngren eventually became one of the most well-known and popular Swedish writers of the 18th century. She died of breast cancer and is buried in the cemetery of Klara kyrka in Stockholm; her collected poems were, by her instructions, published by her husband under the name Attempts of Poetry in 1819.