SDKÚ period

Beblavý became a member of the Slovak Democratic and Christian Union – Democratic Party (SDKÚ) in 2009 and got elected MP on the party list in the 2010 Slovak parliamentary election. As an MP, he managed to implement several partial reforms such as mandatory online publication of final theses at the Slovak universities and more transparency in allocation of European funding.^[4][5]

In the 2012 Slovak parliamentary election Beblavý again ran on the list of SDKÚ, which was at the time heavily implicated in the corruption allegations known as the Gorilla scandal. Beblavý was not personally involved in the scandal, however the party ended up performing poorly in the election losing 17 out of its previously held 28 parliamentary seats. Nonetheless, Beblavý managed to preserve his seat due to receiving over 15,000 personal votes under Slovakia's optional preferential voting system.

With regards to the Gorilla scandal Beblavý at first supported the party leadership, while insisting on a thorough investigations of the allegations.^[6] However, in 2013 he joined the group of rebel MPs led by Lucia Žitňanská who left the party over its associations with disreputable characters.^[7]

Sieť and Spolu period

In 2014, Beblavý joined the newly established Sieť party founded by a fellow MPs Radoslav Procházka a defector from the Christian Democratic Movement and Andrej Hrnčiar who was originally elected on the Most–Híd party list. Beblavý got elected deputy chairman of the new party but unlike the Procházka and Hrnčiar, he did not give up his mandate and remained MP for the rest of the term.^[8] As the sole Sieť MP, Beblavý managed to get legislation approved to greatly liberalize the mortgage market in Slovakia, resulting in a rapid decline in mortgage interest rates^[9] and - according to the some claims - fueling growth of household debt and real estate prices.^[10] He also raised awareness about many cases of corruption and irregularities in the public sector.^{[11][12][13][14]}

In the 2016 Slovak parliamentary elections, Sieť severely underperformed the polls and with 5.6% of votes barely passed the 5% representation threshold. Beblavý himself, however, retained his seat. Soon after the election, Procházka agreed to join the coalition with the Direction – Slovak Social Democracy in spite of promises made before the election. Beblavý considered this alliance a betrayal of the voters and left the party along with two other Sieť MPs - Simona Petrík and Katarína Macháčková.^[15]

Over the course of 2017 and 2018 Beblavý and two other two Sieť rebels teamed up with defector MPs from other parties - Jozef Mihál from the Freedom and Solidarity party and Oto Žarnay from Ordinary People and Independent Personalities to start a new party called Together – Civic Democracy (Spolu). Beblavý became the chairman of the new party.^[16] While leading Spolu, Beblavý remained an active MP, notably leading an initiative to stop import tax fraud scheme, which led to the resignation of the high-profile head of Slovak Financial Administration authority František Imrecze.

Spolu formed an electoral coalition with another newly formed party, Progressive Slovakia. The coalition appeared to have a momentum at first, winning the 2019 European Parliament election with over 20% of the vote. Nonetheless, in underperformed polls in the 2020 Slovak parliamentary election, gaining 6.96% of the vote, just a few hundred votes short of the 7% representation threshold for election coalitions. The party consequently lost all its MP seats, including Beblavý's. Soon after the election, Beblavý, who co-led the list with Progressive Slovakia leader Michal Truban, resigned his party chairmanship and retired from politics.^[17] Polls show that PS would have entered parliament without the coalition.^[18]