Xavi's side entered the contest 11 points clear of second-placed Real Madrid, and their success over Espanyol has moved them 14 points ahead of Los Blancos in the table, so they cannot be caught at the summit.
Barcelona were two goals ahead inside the opening 20 minutes of the derby, with Alejandro Balde setting up Robert Lewandowski for the opener in the 11th minute, before the former got his name on the scoresheet by converting a cross from Pedri, leaving Espanyol with a mountain to climb in the league affair.
Lewandowski then made it 3-0 in the 40th minute by tapping a low Raphinha cross into the back of the net from close range, and the title celebrations could begin early in the second half when Jules Kounde made it four by nodding into the back of the net from a deep Frenkie de Jong pass.
There was a response from relegation-threatened Espanyol, with Javi Puado registering in the 74th minute, but it was always going to be a case of too little, too late from the hosts, who then added a second in stoppage time through Joselu.
Barcelona again disappointed in Europe this season, failing to progress past the group stage of the Champions League before losing to Manchester United in the Europa League knockout round playoffs, while they were eliminated by Real Madrid in the semi-finals of the Copa del Rey.
However, the Catalan outfit have won their first La Liga title since 2019, with an excellent campaign seeing them collect 85 points from their 34 matches to date.
Barcelona now have four pressure-free games against Real Sociedad, Real Valladolid, Mallorca and Celta Vigo to finish the campaign, but Espanyol still have plenty to fight for, with the Catalan outfit 19th in the table, four points from the safety of 17th position.
Xavi's side are not actually the leading goalscorers at this stage of the campaign, netting 64 to Real Madrid's 70, but they have only conceded 13 times in their 34 matches, with their strong defence proving to be a key part of their success.
A big summer awaits for the club, meanwhile, as they attempt to boost their squad with the acquisition of new signings, although the majority of those could come from the free agent market.