Gianni started his career at Argentinos Juniors aged 18 in 2000, making his professional debut in a 1–0 loss against Rosario Central.
In 2005, he returned to Argentinos and in the next season, Gianni won experience in Primera División, scoring his first goal for this tournament against Banfield in the penultimate week of the Torneo de Clausura 2006.
On 26 June 2008, Gianni was loaned to the Chilean team Universidad Católica, he arrived to the precordilleran club with the mission of replace to his countrymen Darío Bottinelli.
He also was recommended to the coach Fernando Carvallo by the former footballer Jorge Quinteros, who had a great pass in this team in 2005.
Quinteros including talked with Gianni and was very eager to play for Católica, affirmed the former striker of the UC.