Mahrez has scored 17 goals and made 11 assists in 34 league games to take Leicester to the cusp of the title.
The award was voted for by the Algeria international's fellow professionals.
Tottenham midfielder Dele Alli, 20, was named PFA Young Player of the Year, while Manchester City forward Izzy Christiansen won the Women's Player of the Year award.
Sunderland striker Beth Mead, 20, was named Women's Young Player of the Year.
Analysis: 'I voted Vardy but Mahrez deserves it'
Mahrez, 25, held off competition from Tottenham forward Harry Kane, Arsenal midfielder Mesut Ozil, West Ham United midfielder and fellow Leicester men Jamie Vardy and N'Golo Kante to win the award.