Judge Richard May said Plavsic participated in crimes of "utmost gravity" during the 1992-95 war in Bosnia and that "undue lenience would be misplaced."
But the court gave her credit for pleading guilty and helping to bring peace and reconciliation after the war.
Plavsic, 72, is the highest-ranking politician from the former Yugoslavia to be sentenced by the court so far. Former Yugoslav President Slobodon Milosevic is on trial before the same tribunal of three judges, but that case is expected to continue for another year.
The court said it took into account Plavsic's advanced age and the testimony on her behalf by former Secretary of State Madeleine Albright and others, who said she had played an important part in carrying out the peace agreement negotiated in 1995 in Dayton, Ohio.
At the same time, Plavsic, who was second only to wartime Bosnian Serb leader Radovan Karadzic, closed her eyes to murder, torture and plunder, the court said.
Plavsic later became president of Bosnian Serb republic from 1996-98.
"The crimes were of the utmost gravity. That is the starting point for the determination of sentence," May said. "Having given due weight to the factors set out, the Trial Chamber sentences you to a period of 11 years."
Experts estimate that more than 200,000 people were killed in the Bosnian war, the worst carnage seen in Europe since World War II, as Serbs led a campaign to drive out Muslims and Croats from Serb-dominated areas and create a unified greater Serbia.
May recounted that Bosnians were "mistreated, raped, tortured and killed" in a campaign of ethnic cleansing that Plavsic embraced and promoted.
"No sentence which the trial chamber passes can fully reflect the horror of what occurred or the terrible impact on thousands of victims," May said.
In an arrangement with the prosecution, Plavsic pleaded guilty last October to one count of persecution of Muslims and Croats. In exchange, prosecutors dropped seven other war crimes charges, including two counts of genocide.
The charge carried a maximum penalty of life in prison. But at age 72, Plavsic has said almost any prison term could amount to life. She is the only woman indicted by the tribunal.
In her testimony in December, Albright said Plavsic surprised her when the two met in 1997 and Plavsic indicated that she wanted to help implement the peace agreement negotiated in Dayton.
"We talked at some length about what her intentions were. And it was at that point that it became evident to me that she understood all the things that had gone wrong," Albright said. Plavsic indicated she wanted to implement the peace agreement in a democratic way and "was doing it at some risk to herself."
Still, Plavsic continued clinging to the core of her political ideology. "She's a pro-Serb nationalist. I think that's very evident," Albright said.
Albright said that during their post-Dayton talks, she found Plavsic "to be a very conflicted individual" as she struggled to protect the Serbs while carrying through the Dayton plan which sought to balance the interests of Muslims and Croats in Bosnia.
She argued that Plavsic's guilty plea could help victims find closure and move on with their lives.
The Dayton accords ended one of four wars that wracked Yugoslavia under the Milosevic's rule, first as Serbian president and then as leader of all of Yugoslavia. He was also a force in conflicts in Slovenia, Croatia and Kosovo.