Moore gained recognition in the mid-1990s when he embarked on a crusade to display the Old Testament laws in his Etowah County courtroom, inspiring Christians to fight for similar displays in other states.
Although his famous plaque wasn't on display on Monday, he said it would be unveiled in due time.
"God's law will be publicly acknowledged in our court," Moore promised.
Outgoing Chief Justice Perry Hooper Sr. administered the oath of office to Moore in a packed chamber of the Supreme Court, which now has an 8-1 GOP majority.
Moore said his duty as chief justice is "not only to maintain the honor and integrity of the court system and the judicial branch, but to restore and preserve the moral foundation of our law."
A West Point graduate and Vietnam veteran, Moore supports prayer in school and opposes abortion and homosexuality as sins. He has written verse in his free time referring to the United States as a nation that has become a "moral slum" as it banished God from public view.