The three-year agreement with the UK club includes a minimum financial guarantee that is said to be a rugby league record.
Saints chief executive Sean McGuire said: "By creating a brand alliance that will add significant value to both of our organisations we have taken the usual sports sponsorship deal far beyond the traditional relationship.
"We will be taking advantage of Earth's expertise in the area of customer relationship management, while Earth will employ an individual based at Saints to maximise the value of their investment.
Saints' new kits, which will be unveiled in January, will display the Earth Money logo.
