Born in Antofagasta, Toselli joined Universidad Católica youth ranks in 2001, being promoted to first-team by the coach Jorge Pellicer in 2006 for the Torneo Apertura, due to the departure of second-choice keeper Rainer Wirth to Deportes Temuco. The following year, after a notable performance in the FIFA U-20 World Cup, he made his club debut on 25 November, during a 3–0 home win to Coquimbo Unido played at San Carlos. The next season, he was challenging the goal with record-man José María Buljubasich, becoming the first-choice keeper, after their mistakes and its departure to Olimpia.

After of his U-20 World Cup performances, he was nominated to the Toulon Tournament of France two years consecutively (2008–2009). In 2008, Toselli was nominated by the coach Marcelo Bielsa and once was Chile’s outstanding goalkeeper, being runner-up of the tournament with Chile, after of be defeated 1–0 by Italy. In 2009, he was once again nominated to play the Toulon Tournament, which Chile would win, suffering a six-month injury in the final against the France, which Chile won 1–0 with a goal from Gerson Martínez at 86th minute.

On 5 December 2010, Toselli played in the Primera División final match against Everton, where his club was consecrated champion after defeat 5–0 to Viña del Mar based–team at home.

On 11 May 2011, he recovered his titularity under orders of Juan Antonio Pizzi after a terrible mistake of Garcés in a Copa Libertadores quarterfinals match against Peñarol at Montevideo, where inexplicably dropped the ball, which Alejandro Martinuccio take the opportunity for score the definitive 2–0 in the 90th minute. After losing against Universidad de Chile the playoffs finals of the Torneo Apertura, was installed again as starter keeper with the new coach Mario Lepe, after the departures of Pizzi and Garcés. On 16 November, Toselli won the Copa Chile final to Magallanes, being that his second title at Católica, that qualified his team 2012 Copa Sudamericana, which Los Cruzados were eliminated on semifinals against Brazilian side São Paulo after two draws, where Toselli had very well performances.