"Football has been my love and passion my entire life," he wrote on Twitter. "I was raised to play QB, and I very much look forward to dedicating 100 (percent) of myself to being the best QB possible and winning NFL championships.
"I have started an extensive training program to further prepare myself for upcoming NFL workouts and interviews. I eagerly await the opportunity to continue to prove to NFL decision makers that I am the franchise QB in this draft."
Oakland drafted Murray with the ninth overall pick last June. The club agreed to let him play football during his junior year at Oklahoma before requiring him to report to the A's.
Murray spent the past few weeks trying to decide between the two sports after thriving on the gridiron.
At the end of the college football season, he talked about pursuing both sports simultaneously. However, the time demands of being an NFL quarterback would have made that dream nearly impossible.
Deion Sanders and Bo Jackson are the highest-profile dual-sport stars, as both played baseball and football at the same time in the 1990s.
Murray was already slated to attend the NFL Scouting Combine at the end of February, where he'll be one of the most watched prospects. The 21-year-old could be a first-round pick in the NFL draft in April, which would make him the first athlete selected in the first round of the MLB and NFL drafts, according to the NFL's research department.
The 5-foot-10 pivot electrified the country during his lone campaign as a starter at Oklahoma, throwing for 4,361 yards with 42 touchdowns and only seven interceptions. He added 1,001 yards and 12 touchdowns on the ground.