Maede Soltani, who lives in Germany, said her family was officially notified Monday of last week's ruling, which came during the appeals process.
Her father, Abdolfattah Soltani, co-founded a human rights group with Iranian Nobel Peace Prize laureate Shirin Ebadi. He was arrested last year.
A court in March initially sentenced the 58-year-old to 18 years in prison on various charges, including co-founding the Center for Human Rights Defenders, spreading anti-government propaganda and endangering national security.
"My father was told that his sentence would be reduced (further) if he would apologize and speak out against Ms. Ebadi in an open letter or an interview," Maede Soltani said. "He declined."
Amnesty International maintains Soltani is a "non-violent political prisoner who is being jailed only for his legitimate activities" as a human rights lawyer.
"Abdolfattah Soltani is one of the bravest human rights defenders in Iran," the group said after his detention last September, urging his immediate release.
Maede Soltani told The Associated Press on Tuesday that last week's "politically motivated" ruling cannot be appealed a second time.
Soltani was previously arrested for seven months in 2005 and again for several months in the wake of Iran's disputed presidential elections in 2009.
The revolutionary court also upheld the decision to transfer Soltani to a remote prison in the city of Borazjan, about 1,000 kilometers (620 miles) southwest of Tehran, Maede Soltani said, adding that the family will barely be able to visit him there.
Working alongside Ebadi, the lawyer also represented the family of photojournalist Zahra Kazemi, a Canadian of Iranian origin who was arrested for taking photographs in front of Evin prison and died several days later in the prison, possibly after being tortured.