They replace Celtic chief executive Peter Lawwell and Partick Thistle managing director Ian Maxwell, who move to the SFA's professional game board.
The changes were implemented at the SPFL's annual general meeting.
Robertson and Gray join Hearts' Ann Budge as the top-flight clubs' board representatives.
They will serve alongside SPFL chief executive Neil Doncaster, new chairman Murdoch MacLennan and independent non-executive Karyn McCluskey, along with Falkirk's Martin Ritchie and Morton's Warren Hawke serving the Championship clubs and Stranraer's Iain Dougan representing the League One and Two clubs.
Rangers managing director Stewart Robertson and Hamilton chairman Les Gray have joined the board of the Scottish Professional Football League.