Her husband, Reza Khandan, said the Iranian authorities brought his wife home on September 18 and told her she did not need to go back to jail to serve the rest of her prison term.
Sotoudeh was serving a six-year sentence, after being arrested in 2010 and convicted on a number of charges including acting against Iran's national security.
She was reportedly released along with several 11 other political prisoners, including Mohsen Aminzadeh, a reformist former deputy foreign minister.
Her release follows the election of Iran's new president, Hassan Rohani, who has promised moderation and more rights for Iranians. Rohani travels to New York to attend the United Nations General Assembly next week.
Khandan told AP the family had expected Sotoudeh to come home for a short leave, but "they have told her she is free."
He said the authorities gave Sotoudeh no explanation for her release.
Iran's ISNA news agency said Sotoudeh had been pardoned and freed from prison.
It said the other people released were detained after the unrest that followed the disputed 2009 reelection of former President Mahmud Ahmadinejad.
The Iranian opposition website Kaleme reported that seven other female political prisoners have been released.
Sotoudeh is an outspoken human rights lawyer known for taking high-profile cases, defending journalists and rights activists, including Nobel Peace laureate Shirin Ebadi.
After her arrest in 2010, she was initially sentenced to 11 years in prison for "propaganda against the regime" and "acting against the national security." An appeals court later reduced her sentence to six years, which she was serving at Tehran's Evin prison.
Activists and campaigners have said the charges against her were fabricated because of her human rights activities.
In 2012, the European Parliament gave its most prestigious award, the Sakharov Prize for Freedom of Thought, to Sotoudeh and acclaimed Iranian filmmaker Jafar Panahi.
European Parliament member Marietje Schaake, who had nominated Sotoudeh for the Sakharov Prize, told RFE/RL: "It's really exciting, a very important first step to put actions behind the words of the promise and the ambition of more openness and more respect for the rights and freedoms of the people of Iran."
Amnesty's Middle East and North Africa Deputy Director Hassiba Hadj Sahraoui said the release of Sotoudeh and others must mark "a fundamental shift in Iran’s policies on human rights and the way the authorities deal with peaceful activists and critics."
Otherwise, she said, it risks being seen as a calculated public relations stunt ahead of the UN meeting.
In a statement, the International Campaign for Human Rights in Iran welcomed the releases and urged Rohani to continue to take concrete steps toward improving the country's "urgent human rights situation" ahead of his scheduled UN speech on September 23.
Marie Harf, a deputy spokeswoman at the U.S. State Department, said the United States also welcomed Sotoudeh's release.
While in prison, Sotoudeh repeatedly went on hunger strike in protest at her arrest and at being deprived of her rights while in jail, such as access to her lawyer and family.
Last year, she held a hunger strike for nearly 50 days to protest official harassment of her relatives, after her husband and 12-year-old daughter were subjected to a travel ban.
The United Nations, European Union, and the world's main international human rights groups had called for Sotoudeh to be freed, calling her a prisoner of conscience.