The Book of Daniel identifies the Prophet Daniel as its author.
Daniel 9:2, Daniel 10:2
Jesus also considered the Prophet Daniel to be the author.
Matthew 24:15
It is believed to be written between 540 and 530 B.C.

Daniel was a Jewish prophet during the reign of the Kings Joiakim and Zedekiah of Judah 508-586 B.C. and the time of the Jewish exile and served God through the reign of King Nebuchadnezzar of Babylon (605-562 B.C.)
and during the reign of Cyrus the Great, founder and ruler of the Persian empire (559-530 B.C.).