Gillislee was released on Saturday by the New England Patriots despite accumulating 960 yards and 13 touchdowns the past two years.
Second-year player Alvin Kamara is solidly entrenched as the starter, but the Saints will be without Mark Ingram for the first four games of the regular season due to a suspension.
The signing of Gillislee gives the Saints another viable offensive weapon. In a game against New Orleans last season, Gillislee gained 69 yards and scored one touchdown on a season-high 18 carries.
New Orleans, which is at the 53-man roster limit, has yet to announce a corresponding move.