The 35-year-old, currently playing at Chesterfield after making over 500 appearances for Hartlepool, has been a member of the PFA management committee for a number of seasons.
Carlisle was forced to relinquish the role after announcing his retirement from professional football, and Humphreys will officially be appointed at the PFA AGM in November.
Humphreys said: "I am honoured to have been elected by my fellow members of the management committee and look forward to taking up the position of PFA chairman at the AGM in November.
"I am fully committed to the role that the PFA plays across all areas of football and will make every effort to continue the great work which Clarke has put in during his time as chairman."
Humphreys started his career with Sheffield Wednesday and joined Hartlepool in 2001, making 548 senior appearances in 12 years at the club before being released at the end of last season.
PFA chief executive Gordon Taylor said: "We congratulate Ritchie on his selection as chairman and feel sure his vast experience as a player and management committee member make him eminently suitable for the position.
"We look forward to working together in the future development of the PFA and also wish to thank Clarke Carlisle for his outstanding contribution to the PFA as a player, management committee member and chairman and wish him every success in the future."
Carlisle also offered his support to his successor, adding: "I have known and worked with Ritchie over a number of years and feel confident that he possesses the necessary skills and experience to take on this role.
"I wish him all the best and I am sure he will play a real part in shaping the PFA for the future."