Members of his new cabinet, who include technocrats, veteran politicians and ministers held over from the previous government, each took the oath of office.
During Catalonia's last election in December that year, the Socialists came fourth but have risen in the polls since Illa's unexpected nomination in December.
While the BSP has dismissed the inflation uptick as "transitory", some economists have ruled out further policy easing this year and have raised the possibility of a rate hike.