A Tucson jury found Shawna Forde, 42, guilty of murder in the May 2009 killings of Raul Flores, 29, and his daughter Brisenia at their home in Arivaca, a desert community 10 miles north of Mexico.
The jury deliberated for seven hours over two days. Forde was convicted on two counts of first-degree murder, attempted first-degree murder for the shooting of Flores' wife and related aggravated assault and robbery counts.
The jury will return to Pima County Superior Court on Tuesday to decide if the death penalty should be considered.
Forde had pleaded not guilty.
Her attorney, Eric Larsen, argued that Forde was never inside the home. Prosecutors disputed that contention, saying Forde was the ringleader if the operation and the law is clear.
"She didn't put a gun to Brisenia's head ... but she was the one in charge," prosecutor Rick Unklesbay told jurors. "Because of that you must hold her accountable."
Larsen said Forde talked a big game, but "she frankly just didn't have the wherewithal to do this."
Calls seeking comment from Larsen on Monday were not immediately returned.
Forde is the leader of the Minutemen American Defense, a small border watch group. Prosecutors argued that she planned the attack to help fund its anti-immigrant operations.
Authorities said Forde and two men dressed as law enforcement officers, forced their way into Flores' home then shot him, his daughter and wife, Gina Gonzalez, who survived her injuries after getting into a gun battle with the attackers.
Flores was believed to be involved with drug trafficking, police said, but officers don't think the assailants found much cash or drugs in the home.
A 911 recording released by the Pima County sheriff's office captured Gonzalez pleading for help after her husband and daughter were shot. She was heard crying out in pain from a gunshot wound then becoming frantic as the attackers returned.
The sound of nine gunshots was heard as Gonzalez engaged the intruders.
"Oh my God, I can't believe they killed my family," Gonzalez said on the recording.
Police said Gonzalez shot and wounded one of her attackers, Jason Eugene Bush, who officers believe was the gunman.
Another man, Albert Robert Gaxiola, is accused of providing information about the area.
Bush and Gaxiola go on trial in the spring.
Before coming to Arizona, Forde lived in Everett, Wash., where she ran for the City Council in 2007, promising to allow police to check the immigration status of suspects, according to news accounts.
Chris Simcox, founder of the Minuteman Civil Defense Corps, said his group expelled Forde in 2007 amid allegations of lying and pretending to be a senior leader. Forde began her own group, bragging that it would be going after drug cartels, he said.
"We knew that Shawna Forde was not just an unsavory character but pretty unbalanced, as well," Simcox said.