Necho II (sometimes Nekau, Neku, Nechoh, or Nikuu; Greek: Νεκώς Β'; Hebrew: נְכוֹ, Modern: Neḵō, Tiberian: Nəḵō) of Egypt was a king of the 26th Dynasty (610–595 BC), which ruled from Sais. Necho undertook a number of construction projects across his kingdom. In his reign, according to the Greek historian Herodotus, Necho II sent out an expedition of Phoenicians, which in three years sailed from the Red Sea around Africa to the Strait of Gibraltar and back to Egypt. His son, Psammetichus II, upon succession may have removed Necho's name from monuments.

Necho played a significant role in the histories of the Neo-Assyrian Empire, the Neo-Babylonian Empire and the Kingdom of Judah. Necho II is most likely the pharaoh Necho who was mentioned in 2 Kings, 2 Chronicles, and Jeremiah of the Bible. The aim of the second of Necho's campaigns was Asiatic conquest, to contain the westward advance of the Neo-Babylonian Empire, and cut off its trade route across the Euphrates. However, the Egyptians were defeated by the unexpected attack of the Babylonians and were eventually expelled from Syria.

The Egyptologist Donald B. Redford observed that Necho II was "a man of action from the start, and endowed with an imagination perhaps beyond that of his contemporaries, [who] had the misfortune to foster the impression of being a failure."

Necho II was the son of Psammetichus I by his Great Royal Wife Mehtenweskhet. His prenomen or royal name Wahem-Ib-Re means "Carrying out [the] Heart (i.e., Wish) [of] Re." Upon his ascension, Necho was faced with the chaos created by the raids of the Cimmerians and the Scythians, who had not only ravaged Asia west of the Euphrates, but had also helped the Babylonians shatter the Assyrian Empire. That once mighty empire was now reduced to the troops, officials, and nobles who had gathered around a general holding out at Harran, who had taken the throne name of Ashur-uballit II. Necho attempted to assist this remnant immediately upon his coronation, but the force he sent proved to be too small, and the combined armies were forced to retreat west across the Euphrates.^{[citation needed]}

In the spring of 609 BC, Necho personally led a sizable force to help the Assyrians. At the head of a large army, consisting mainly of his mercenaries, Necho took the coast route Via Maris into Syria, supported by his Mediterranean fleet along the shore, and proceeded through the low tracts of Philistia and Sharon. At Megiddo (according to 2 Kings 23) he engaged the Judean king, Josiah, and had the Judean king killed (an alternative version, in 2 Chronicles 35, of a battle in Megiddo also exists.)

Herodotus reports the campaign of the pharaoh in his Histories, Book 2:159:

Necos, then, stopped work on the canal and turned to war; some of his triremes were constructed by the northern sea, and some in the Arabian Gulf (Red Sea), by the coast of the Sea of Erythrias. The windlasses for beaching the ships can still be seen. He deployed these ships as needed, while he also engaged in a pitched battle at Magdolos with the Syrians, and conquered them; and after this he took Cadytis (Kadesh), which is a great city of Syria. He sent the clothes he had worn in these battles to the Branchidae of Miletus and dedicated them to Apollo.

Necho soon captured Kadesh on the Orontes and moved forward, joining forces with Ashur-uballit and together they crossed the Euphrates and laid siege to Harran. Although Necho became the first pharaoh to cross the Euphrates since Thutmose III, he failed to capture Harran, and retreated back to northern Syria. At this point, Ashur-uballit vanished from history, and the Assyrian Empire was conquered by the Babylonians.