On 18 July 2015, Hadházy was elected to the LMP's leadership. He launched a portal korrupcioinfo.hu and held weekly press conferences, where uncovered numerous alleged corruption cases involved Fidesz politicians and government—close businessmen and bankers. After the LMP's most well-known politician, András Schiffer announced his retirement from politics, Hadházy was elected co-chair of the party on 16 July 2016, alongside Bernadett Szél. He was also elected a Member of Parliament via the party's national list on 12 September 2016, replacing Schiffer. There he became a member of the Legislative Committee. Hadházy criticized the Orbán government's migrant quota referendum campaign in October 2016; he called the referendum as "destructive", because it "whipped up panic-like fear" among the citizens, while distracting from the "collapsing health care" and the "looting of EU funds at state level". He also said Orbán "isolated himself internationally with his populist campaign of provocation".