The new leader will replace Choo Mi-ae, a five-term lawmaker.
The DP clinched a sweeping victory in the June 13 local elections and parliamentary by-elections. Winning 11 out of 12 districts contested, the party now controls 130 seats in the 300-member National Assembly.
The DP has cautioned against possible complacency after the election victory, vowing to enforce its pledges from the local elections and back up the Moon Jae-in government's drive for reforms.
The party called for swift normalization of the National Assembly to prevent a prolonging of the vacuum left by the departure of the parliamentary speaker.
Former National Assembly Speaker Chung Sye-kyun's two-year term ended last month, but rival parties failed to even start work to pick his successor and form 18 standing committees.
The main opposition Liberty Korea Party suffered a crushing defeat in the elections, throwing into question what path the conservative party will pursue in its efforts to regain public trust.
"I hope that opposition parties join efforts to normalize the National Assembly by taking into account the public sentiment that was revealed in the outcome of the elections," Hong Yong-pyo, the floor leader of the DP, said at the start of a party meeting with senior officials.
He said that discussions over the formation of the parliamentary committees may be possible as early as this weekend after rival parties complete internal shake-ups.
"The DP will make efforts to swiftly handle tasks related to peace and people's day-to-day issues," Hong added. "We will put the National Assembly back on track as soon as possible."(Yonhap)