The Northwestern graduate, who was jailed in Iran for three months this year on charges she was a spy for the U.S., took part in a rally calling for "freedom in Iran."
She told the crowd that protests and gatherings like the "Global Day of Action" at Federal Plaza are illegal in Iran.
"I learned of this power of international support when I was in prison," Saberi said. "It gave me strength and hope, and I realized I was no longer alone."
Organizer held the event in 105 cities around the world in hopes of drawing attention to the violence and unlawful arrests covered by the media in the wake of the recent controversial presidential election.
"To the people of Iran, we want you to know you are not alone. You have a whole world of supporters behind you," Saberi said. "We are watching, and we stand with you."