The news was confirmed in a statement to the London Stock Exchange, hours after former chairman Malcolm Murray and fellow non-executive director Phil Cartmell left the Ibrox board.
Easdale, who is described on the club's website as "an entrepreneur and a director of several businesses", has a business empire which includes McGill's Bus Service Limited.
The 42-year-old said: "As a lifelong Rangers supporter, I am proud and honoured to serve on the board of such a great sporting institution and look forward to helping Rangers Football Club continue its journey back to the top of Scottish football."
The Greenock businessman and his brother Sandy confirmed in May their intention to increase their Rangers shareholding and seek a significant say in the running of the club.
The pair invested in the Light Blues last year and are in line to buy former chief executive Charles Green's shares when he is free to sell them under stock exchange rules.
In another day of boardroom shuffles at Rangers, Murray sealed his departure from the Glasgow giants as Easdale's appointment to the board was confirmed.
Murray stepped down as chairman in May, amid speculation of moves to oust him.
He was replaced in the role by ex-Gers boss Walter Smith in what was a unanimous decision by the rest of the board and a move aimed at bringing stability to the club.
Smith - who returned to Rangers as a non-executive director in November after two spells as manager - said in a statement: "Both Malcolm and Phil have made important and valuable contributions to the club.
"The last year has presented the club with a number of challenges and it has been beneficial to have two highly experienced non-executive directors such as Malcolm and Phil offering assistance.
"On behalf of the board I would like to thank them for their considerable efforts in helping to rebuild Rangers.
"Both men have other significant business interests and we wish them well in their future endeavours."