Born in San Diego, California, Macready received a bachelor's degree in economics from Stanford University in 1912.

He quickly rose to the position of flight instructor at the Army Pilot School at Brooks Field, Texas.

While based at Brooks Field, Lieutenant Macready wrote a basic flight manual for student pilots, The All Thru System of Flying Instructions.

[2][4] On September 28, 1921, he climbed to 40,800 feet (12,400 m) in an experimental Packard-Le Père LUSAC-11 biplane designed and modified at McCook Field with a special breathing apparatus to provide him oxygen during his ascent.

[4][5] October 5, 1922 Macready and Lieutenant Oakley G. Kelly set a world endurance record of 35 hours, 18 minutes and 30 seconds.

[2] On 13 June 1924, while he was making a night airways flight from McCook Field to Columbus, Ohio and back, his engine died just as he was approaching Dayton.