After receiving a classical education with honors, she debuted as an actress on Italian television in January 2009 with the television miniseries Il bene e il male ("The Good and the Bad"), followed by a starring role in the prime-time miniseries L'uomo che cavalcava nel buio ("The Man Who Rode in the Dark").
　　On December 18, 2009 she made her debut in cinema with the film Io e Marilyn (Marilyn and I) directed by Leonardo Pieraccioni, where she played the role of Martha, daughter of Gualtiero Marchesi, who was played by the director.
　　In 2010, aged 20, she became one of the few Italian actresses to land a role in Hollywood. Gastini appeared with Anthony Hopkins and Colin O'Donoghue in the American film The Rite, directed by Mikael H?fstr?m and produced by New Line Cinema in Los Angeles.