Who was Darius? He probably was not one of the later emperors of the Persian Empire, but his name may have been an alternate name for Gabaru, the governor of Babylon after its fall.
Daniel was retained as one of the three top administrators and did so well that he was considered for the position of grand vizier. Daniel's enemies decided to embarrass him at the point of the law of his God. These laws were basically different from those of Persia's polytheism.
A legal trap was set. By the use of flattery, the wise men convinced Darius to issue a decree outlawing any worship that was not directed to idols or to the king.
When Daniel heard of the decree, he knew that he was the target with all other God-fearing Jews. Deliberately, Daniel went home and prayed to God as usual; he was caught in the act of worship.
The disobedience was reported to Darius who immediately saw the hidden agenda behind the request for the decree. The king tried desperately to find a loophole in the law but could not. Daniel's enemies forced the king to condemn Daniel to death in the lion's den.
Darius was not an intolerant man, and as Daniel was thrown into the den, the king expressed a wish that Daniel's God would somehow come to the rescue.
Darius spent a sleepless night, deeply distressed about Daniel's plight. At dawn he unsealed the den and cried out in anguish, seeking whether the living God had saved Daniel's life. His request was a mixture of dread and wavering faith. Daniel's voice came booming back. He was alive because God's angel had muzzled the lions. Daniel's faithfulness and innocence had been honored by his God. Daniel was taken unharmed from the den. His trust in the one true and just God had not been misplaced, just as in the case of the three Hebrews in the furnace.
Darius gave evidence of his new faith by condemning Daniel's accusers to death in the same lion's den. Neither the deities of these men nor their vaunted and mysterious skills could save them.
On the other hand, Darius issued a new decree throughout the kingdom. The decree was stronger in tone than the one sent by Nebuchadnezzar (3:29); it required that everyone fear and reverence the God of Daniel. The king then affirmed the eternal sovereignty of the true God and his power to save those who worship God, even as he had rescued Daniel.