He conspired against and slew his predecessor, Pekah to become king (2 Kings 15:30). Shalmaneser campaigned against Hoshea, forcing him to submit (17:3), but once Shalmaneser returned home, Hoshea sought the support of "So, the king of Egypt" and withheld his promised tribute. There is some mystery as to the identity of this king of Egypt: some scholars have argued that "So" refers to the Egyptian city Sais, and thereby refers to king Tefnakht of the 24th Dynasty; however the principal city of Egypt at this time was Tanis, which suggests that there was an unnecessary correction of the text and Kenneth Kitchen is correct in identifying "So" with Osorkon IV of the 22nd Dynasty.

The Assyrian king invaded the land a second time, and captured Samaria after a siege of three years. Shalmaneser further wreaked punishment on the kingdom by deporting the citizens of Israel beyond the Euphrates (some 27,290 according to Assyrian records), and settled people from Babylon, Cuthah, Avva, Hamath and Sepharvaim in their place (2 Kings 17:6, 24). The author of the Books of Kings states this destruction occurred "because the children of Israel sinned against the Lord" (2 Kings 17:7), not because of a political miscalculation on Hoshea's part.