Erendis was born to Beregar and Núneth, who were descended from a minor branch in the Númenorean nobility of the House of Bëor. This was a lineage of lesser status then that of the royal house, thus enforcing a shorter lifespan upon her. She and her parents lived in the Númenorean land Emerië, a region she loved dearly.
She was in love with Aldarion for a long while before marrying him. They were betrothed in SA 858 and were finally married in SA 870 and had one child in the spring of SA 873, a daughter they named Ancalimë, the future Tar-Ancalimë who was the first of the Ruling Queens of Númenor. It seemed to Erendis that Aldarion was always away from her, and that she never had enough time with him before he went on another voyage. Aldarion was often late returning from his seafaring, which caused Erendis to suffer. Finally, Erendis became estranged from her husband, so great was her unhappiness with him.
She took her daughter to be raised on her farm in the countryside of her beloved land of Emerië. When Aldarion finally returned, he made decreed that his daughter be returned from her place of dwelling to live with him in Armenelos. Erendis grudgingly did as he commanded, but out of pride she never returned to him, and they were all but divorced SA 882. In SA 985, when she heard that Tar-Aldarion was returning from his last voyage, she apparently drowned herself in the Bay of Rómenna.
Although there appears to be no definitive meaning, the name Erendis may have originated from the Noldorin words er, meaning "one" or "alone", and dîs, meaning "bride", which would be prophetic for the unfortunate events of her life.
Her Quenyan name was Tar-Elestirnë, meaning "Lady of the Star-brow", because of the white gem she set in a silver fillet which Aldarion bound to her forehead. She wore it for many years.