On June 26, 2014, Ennis was selected with the 18th overall pick in the 2014 NBA draft by the Phoenix Suns. He later joined the Suns for the 2014 NBA Summer League. On August 8, he signed his rookie scale contract with the Suns. He made his NBA debut on October 29 in the Suns' season opener against the Los Angeles Lakers, recording two points, three assists and one block in a 119–99 win. During his rookie season with the Suns, Ennis received multiple assignments to the Bakersfield Jam of the NBA Development League.