Hallacar was the son of Hallatan of Hyarastorni, a nobleman of Númenor descended through five generations from King Vardamir Nólimon. He wooed and won the hand of the proudly wilful Queen Tar-Ancalimë. Though the circumstances of their marriage are unclear (there are several contradictory accounts) it seems clear that Ancalimë married for political reasons. In particular, she seems to have been motivated to produce an heir to prevent her cousin Soronto from claiming the throne.
Tar-Ancalimë and Hallacar did indeed produce an heir, who would one day rule as Tar-Anárion, the eighth King of Númenor. After the birth of their son, Hallacar became estranged from the Queen, and they lived apart from one another.