He was Svoboda's campaign manager during its national breakthrough at the 2012 Ukrainian parliamentary election. The Parliament elected him the Deputy Speaker by absolute majority of the vote. During his time in office he co-chaired the Poland-Ukraine interparliamentary group. Koshulynsky actively supported the 2013-2014 demonstrations against the regime of president Viktor Yanukovych and was one of a handful of parliamentary opposition members who remained with the protesters during the police gunfire in February 2014. In March 2014 he stated that the decision to hold Crimea referendum was unconstitutional, citing the absence of Ukrainian legislative framework on local referendums.