Gilman filed a $60 million suit in Manhattan federal court and McNenney filed a $30 million suit in state court.
Spitzer wrote the column in 2010 in response to a Wall Street Journal editorial he said disparaged the cases he brought against Marsh.
Both Spitzer and Slate's editor say the suits are frivolous.
A judge convicted Gilman and McNenney in 2008 of violating state antitrust laws. The convictions were later overturned.