Polgara the Sorceress begins with Ce'Nedra entreating Polgara to write a book about her life, filling in the gaps left by her father's story, Belgarath the Sorcerer. The main part of the story then opens just before the birth of Polgara and her sister.
Polgara and her twin sister Beldaran were raised by their "uncles", the deformed dwarf Beldin and the twin sorcerers Beltira and Belkira (all disciples of Aldur, like Belgarath), after the apparent death of their mother, Poledra. Their mother had been a shape-shifting wolf (that is, she could assume the form of a human woman; but was born and still thought as a female wolf) and was distressed that her human babies would be born lacking in wolvish instinctive knowledge, so she began speaking to and training them telepathically while they were still in her womb. After the birth of the twins, Poledra was presumed to have died, but her daughters knew that she had simply had to go away. She continued to speak to Polgara, who throughout her life maintained a close relationship with her mother.
Polgara and Beldaran were identical twins, but Aldur and their mother made physical changes directed at Polgara while they were still in the womb. Beldaran was fair-haired and Polgara was dark. According to various historical dates listed in Belgarath the Sorcerer and Polgara the Sorceress we are able to determine that Polgara and Beldaran were born in the year 2000 A.C. (Alorn Calendar). Polgara was born first, but Beldaran was the dominant twin. Soon after her birth, her father, Belgarath, touched her forehead in a gesture of welcome to his first-born which was also a symbol to which his original race performed on their first born. One lock of her hair turned silver, marking her forever as a sorceress.
For many years, Polgara hated her father, in part because her mother's wolf instincts could not understand his apparent abandonment during her pregnancy, and sensitive Polgara had picked up on this, and in part because, as he believed his wife dead, Belgarath had left for years, wandering from vice to vice in poor mental condition. When Belgarath returned to take care of his daughters, Beldaran was quick to forgive him but Polgara often fled to the Tree at the center of the Vale of Aldur, where she befriended and learned to speak to birds. It was there that she first learned how to access her powers as a sorceress. She learned to shift into the form of an owl, a shape she learned from her mother.
Belgarath (with Beldaran's help) eventually negotiated an uneasy peace, and Polgara began her academic training. Eventually, it was revealed that one of the twins was to wed Riva, the king of a newly formed subdivision of the Alorn kingdom of Aloria. Beldaran was chosen, as indeed this was her role in the ongoining War of Destinies. Polgara bitterly resented the "loss" of her sister, who had been the center of her life, but the shared loss eventually brought father and daughter closer together, and Polgara was presented for the first time as beautiful Polgara the Sorceress.
Beldaran soon died, but Polgara, as a sorceress and disciple of Aldur, did not age. (Although the male disciples tended to be gray-haired, Polgara remained young.) Over the years, she maintained a relationship with the descendants of Beldaran and Riva that would eventually become her life's work.
A relatively young Polgara spent many years in the Arendish duchy of Vo Wacune. The focus of her work was to end (sometimes by force) the Arendish civil wars. Ultimately she earned the gratitude of the dukes and her own duchy, and she became the Duchess of Erat. She imposed her own particular notions on the people of her duchy, modernizing its government and freeing her serfs. When war broke out again and Vo Wacune was destroyed, Polgara trained her people to become self-sufficient, and eventually what was once Erat became part of the new kingdom of Sendaria, noted for the practicality of its people, and the Duchess of Erat was all but forgotten.
When the Rivan King was killed by assassins, Polgara became the guardian of a secret line of surviving heirs. She became an expert in not being noticed, often living in the towns of Sendaria.
At the Battle of Vo Mimbre, Polgara learned that in the prophecies of the other side, her role was to be the bride of the dark god Torak. Her continued defiance both confused and infuriated him. Her refusal to accept Torak's dominance, due to her previously unrealized love for Durnik, was a key point (an Event) in the fight between the two competing Prophecies.
Following Torak's death, Polgara married Durnik, and the couple returned to Poledra's cottage in the Vale of Aldur. When Garion had to set forth in order to save the world again, both Polgara and her husband, along with their other companions, went with him. After their final victory over Zandramas, Polgara discovered she was pregnant with twins.
Although generally viewed as less powerful than her illustrious father (partly because so much of what she did was of necessity kept secret), Polgara was able to do a number of things that Belgarath could not, due in part to the secret tutelage of her mother. She was better than he at subtle works and had a particularly deft touch with human minds. In 'Enchanters' End Game' however, Polgara in rage at the 'Death' of Durnik threw the full power of her mind at her father, in an attempt to blow past him and seek revenge on Zedar. Her father however held against her full power without his will breaking, though he was upset that he was forced to take such action against her, never having wanted to do so.