We first read of Gideon at a time when "the people of Israel did what was evil in the sight of The Lord; and The Lord gave them into the hand of Midian seven years." (Judges 6:1 RSV). When the time of punishment was completed, The Angel of The Lord appeared to Gideon and said, "Go in this might of yours and deliver Israel from the hand of Midian; do not I send you?" (Judges 6:14 RSV). With some reluctance, and a request for signs that God was truly with him, Gideon finally accepted his calling (Judges 6:17-22).
Gideon's first attack was somewhat modest; under cover of darkness, Gideon and ten of his servants destroyed the people's altar of Baal, and cut down the Asherah pole that had been erected beside it (Judges 6:25-27).
Using a Shofar, Gideon then mustered a force of 22,000 Israelites (Judges 6:34-35). Of that number, God had only three hundred selected (Judges 7:2-7) so that they would know that it was God who delivered them from the vastly larger force that had been troubling them. And so He did; the 300 Israelites obliterated an army of 120,000 Midianites (Judges 7:19-25, 8:10) and drove the invaders back beyond the Jordan.
The memory of this great victory is referred to a number of times in The Bible (1 Samuel 12:11; Psalm 83:11; Isaiah 9:4; 10:26; Hebrews 11:32). It was so complete that the Israelites had peace for 40 years afterward (Judges 8:28) - exceptional for the times.
Gideon died at a good old age, and was buried in the tomb of his fathers. Incredibly, soon after his death the Israelites again drifted back into idolatry and other degenerate behavior, a cycle that would last for centuries until their total defeat and exile, as God allowed - first the Kingdom of Israel (the "Lost Ten Tribes") in the north by the Assyrians in 721 B.C. (see Ancient Empires - Assyria), and then finally the Kingdom of Judah in the southern lands around Jerusalem by the Babylonians in 586 B.C. (see Ancient Empires - Babylon).
Fact Finder: Is Gideon referred to as a man of faith in the New Testament?
Hebrews 11:32-33