Halleck succeeded his father, King Harwyn Hoare, who had conquered the Riverlands and taken them from Storm King Arrec Durrandon. As king, Halleck only visited the Iron Islands three times, which totalled the time span of two years.
Halleck spent the remainder of his time warring against the neighbours of the Riverlands on mainland Westeros. Halleck lost wars against the Kings of the West and the Stormlands. He also failed in three attacks against the Bloody Gate, the bulwark of House Arryn in the Vale. He did, however, succeed in extending his kingdom over Duskendale and Rosby.