O'Malley's endorsement of O'Rourke, who catapulted to the national spotlight in his close Texas Senate race against Sen. Ted Cruz, comes in a column published in the Des Moines Register. O'Rourke hasn't said whether he will seek the White House.
O'Malley says that O'Rourke has "the wisdom to listen, the courage to lead, and a rock-solid faith in the powerful goodness of our nation."
O'Malley abandoned his 2016 campaign after a disappointing finish in the Iowa caucuses. He spent much of the last two years traveling the country in support of Democratic candidates, moves that were widely seen as preparation for another presidential bid.