Murray made the announcement a day after he met with Athletics president Billy Beane and others as they hoped to keep the former Oklahoma quarterback in the fold, per Bob Nightengale of USA Today.
Adam Schefter of ESPN noted that Murray can still play baseball, but is "determined to play football."
The 21-year-old took over as the starting quarterback for the Sooners' football team in 2018 after Heisman Trophy winner Baker Mayfield was selected No. 1 overall in the NFL draft by the Cleveland Browns.
While Murray had big shoes to fill, the Oklahoma offense didn't miss a beat, as he racked up 4,361 passing yards, 42 passing touchdowns and seven interceptions, while rushing for 1,001 yards and 12 more scores.
Murray won the Heisman Trophy for his efforts and led the Sooners to a 12-2 record that included a Big 12 title.
He also took Oklahoma to the College Football Playoff, but it fell to Alabama 45-34 in the semifinal.
Murray originally committed to play both football and baseball at Texas A&M before transferring to Oklahoma in 2015.
After hitting just .122 in his first season with the Sooners, he broke out in a big way during the 2018 season, as he played a strong center field and finished with a .296 batting average, 10 home runs, 47 RBI and 10 stolen bases.
That led to the A's selecting Murray with the No. 9 overall pick in the 2018 MLB draft.
The Athletics and Murray agreed to a deal that paid him a $4.66 million signing bonus, and the A's also gave him their blessing to play one season as Oklahoma's starting quarterback.
By announcing his intention to enter the NFL draft, Murray's pro baseball career with the Athletics may now be in jeopardy.
There is no indication regarding whether he intends to play both football and baseball, but doing so could prove difficult.
Given the success he enjoyed at Oklahoma in 2018, Murray could be in line to be a first-round pick and possibly the first quarterback taken in the 2019 draft.
Murray will likely vie with Ohio State quarterback Dwayne Haskins for that honor, and the potential to be a starting NFL quarterback out of the gates may have been enough to convince Murray to avoid working his way up through the Athletics' minor league system.