Plumlee was selected with the 22nd overall pick by the Brooklyn Nets in the 2013 NBA draft. On July 3, 2013, he signed his rookie-scale contract with the Nets. On November 15, 2013, in his first game against his brother Miles and the Phoenix Suns, he recorded 7 points, 3 rebounds and 2 assists in a 100–98 overtime win. The following night, Plumlee played 26 minutes against the Los Angeles Clippers with both Brook Lopez and Kevin Garnett out injured, and had 19 points and 6 rebounds, both career highs. Plumlee was selected to play in the 2014 BBVA Rising Stars Challenge on Chris Webber's team, while his brother Miles was picked to play on Grant Hill's team. On February 9, 2014, Plumlee recorded his second NBA double-double, finishing with 22 points and 13 rebounds in a Nets victory. On March 17, 2014, both Miles and Mason Plumlee started for the Suns and the Nets, respectively. Mason had 14 points and 11 rebounds, while Miles had 3 points and 6 rebounds in a 108-95 Nets win.