Gillislee was released on Saturday by New England 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.
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 sason-high 18 carries.
New Orleans, which is at the 53-man roster limit, has yet to announce a corresponding move.