Souza was born in Mexico City to a Chilean father and Mexican mother. She lived in Aspen, Colorado until she was eight years old. She studied acting at Centro de Educación Artística, the famed acting school run by Mexican media giant, Televisa, in Mexico City. She also attended acting school in France and completed an intensive summer acting course in Moscow, Russia. In 2008, she completed a Bachelor of Arts in Acting at Central School of Speech and Drama in London. At 22, she returned to Mexico City and began acting in television and film.
In 2009, Souza debuted in the Mexican telenovela Verano de amor, starring singer Dulce Maria, and later starred in Mexican sitcoms Los Héroes del Norte and La Clinica. Her film roles include From Prada, to Nada; in 2013, and two Mexican box office hits, Nosotros los Nobles and Instructions Not Included. In March 2014, Souza landed a regular role as Laurel in Shonda Rhimes' ABC legal drama series How to Get Away with Murder.
In February 2018, Souza appeared in Mexican journalist Carmen Aristegui's show and announced she had been a victim of sexual assault. Souza stated that, when she was 22, she was raped by the director of a TV show she was working in; she did not name her attacker. On April 19, 2018, Souza announced via her Instagram account that she had just given birth to a baby girl from husband since 2014, Marshall Trenkmann. Her pregnancy was kept secret right up to the birth.