The 17-year-old midfielder, who has already made two appearances for the Saints first team, has joined Gary Naysmith’s League Two side on a season-long loan.
City claim to have beaten competition from a number of interested clubs leaving Naysmith delighted with his latest addition.
“Firstly I must thank St Johnstone, and in particular Callum Davidson, for allowing Alex to join us on loan for the season ahead,” he told ECFC TV.
"There was a lot of interest from other clubs in taking Alex on loan so I think it says a great deal about our club that everyone involved at St Johnstone thinks that Edinburgh City is the right club to help with the next stage of Alex’s development.
"Although he is still only 17, Alex has already made his first team debut at St Johnstone and is someone they have high hopes for. Alex will increase and strengthen our options in central midfield and I am looking forward to starting to work with him when he reports for training on Tuesday.”
Ferguson is the third loan player to join the Citizens ahead of the new campaign following the arrival of Hibs striker Ryan Shanley and Livingston goalkeeper Brian Schwake.
“I’m delighted to sign on loan for Edinburgh City and can’t wait to get get to work and be a part of the matchday squad,” Ferguson said.
"I’m hoping to hit the ground running and play as many games as possible for the club, hopefully helping their push for promotion which is something they have been doing over the last few seasons.”