Mr Easdale, who owns the firm with his brother James, made the purchase after former club director Imran Ahmad, who was ejected from the board in April, sold the majority of his 2.2 million shares in the club. A total of 20 separate trades in the club were made yesterday.
Rangers chief executive Craig Mather, consultant Charles Green and finance director Brian Stockbridge are drumming up support in London for the board amid attempts by tycoon Jim McColl to oust key figures.
Mr Easdale and his brother, a board member since July, have long sought to increase their influence at the club and are key allies of Mr Green. The purchase, worth £498,000, brings Sandy Easdale's individual stake to 2.1% - around a seven-fold increase. His wife Gail and brother are also shareholders.
The Easdale family's spokesman, Jack Irvine, said: "We said we would buy more shares and we did. We believe in the future of Rangers Football Club."
Two separate trades of one million shares were made yesterday. It is understood that stockbroker Daniel Stewart, acting for the club, purchased 800,000 shares. No-one at the brokers could confirm this last night.
The sale of Mr Ahmad's stock sale comes after he revealed he is to launch a £3.4 million legal action against the club for unpaid bonuses and legal fees.
Mr Ahmad is named in the Rangers share prospectus as a key employee and locked-in shareholder bound not to sell his shares until December. However, that agreement was made to Cenkos Securities, the club's former stockbroker, which was recently replaced by Daniel Stewart.
Selling to Sandy Easdale guarantees further support for the status quo in the club boardroom as Mr McColl tries to oust Mr Mather, Mr Stockbridge and non-executive director Bryan Smart.
It is not clear whether a place on the board is being cleared for Sandy Easdale, who was jailed in 1997 for VAT offences.