Formation and Ahn–Kim chairmanship (March–July 2014)
The Democratic Party was formed as the New Politics Alliance for Democracy (새정치민주연합; Saejeongchi Minju Yeonhap) on 26 March 2014 after the independent faction led by Ahn Cheol-soo, then in the process of forming a party called the New Political Vision Party, merged with the main opposition Democratic Party, led by Kim Han-gil. Ahn and Kim became joint leaders of the new party. The party performed poorly in by-elections that July, however, and both leaders stepped down, having served for three months. Leadership of the party was assumed by an emergency committee.
Ahn–Moon controversy and split (2015–16)
The next year, at a party convention on February 7, Moon Jae-in was elected the new chairman of the party. Moon, who had previously served as chief of staff for former president Roh Moo-hyun, was the leader of the party's "pro-Roh" faction, which was opposed to Ahn and Kim. Moon came under fire for imposing a "pro-Roh hegemony" in the party, as Ahn and Kim were jeered and harassed at a memorial service for Roh held in May 2015.
The party hemorrhaged support as the factional conflict intensified, falling from around 40 to 30 percent in opinion polls. A survey conducted on November 12–14 showed that supporters of the party wanted Ahn and Seoul mayor Park Won-soon to assume the leadership alongside Moon. On November 29, Ahn rejected a proposal from Moon to establish a joint leadership, and the next month he presented Moon with an ultimatum, demanding that he call a convention to elect a new party leader. Moon rejected the demand, and Ahn left the party.
Ahn was followed by a number of supportive NPAD assembly members, including his former co-leader Kim Han-gil, and the group began preparations to form a new party. On January 12,
Kwon Rho-kap, a former aide of President Kim Dae-jung and a popular figure in the party's traditional stronghold of Honam, also exited the party, similarly citing Moon's "pro-Roh hegemony". Meanwhile, Ahn and Kim merged their group with that of another defector from the NPAD, Chun Jung-bae, to form the People's Party.
Following the defections, the NPAD was renamed the Minjoo Party of Korea, and Moon resigned on 27 January 2016. Moon handed power to Kim Chong-in, an academic and former assemblyman who had more recently served as economic advisor to conservative President Park Geun-hye. Kim was seen as an unexpected choice, as he had previously worked for the right-wing Chun Doo-hwan and Roh Tae-woo administrations in the 1980s, serving as an assembly member for the ruling Democratic Justice Party and as health and welfare minister under Roh.
Under Kim Chong-in (January–August 2016)
Kim Chong-in viewed the pro–Roh Moo-hyun faction and what he considered the extremist wing of the party as responsible for the party's troubles, and pledged to diminish their influence. In the lead-up to the 2016 parliamentary election he moved against key members of the pro-Roh faction in the nominations process, deselecting Lee Hae-chan, who had been Prime Minister under Roh and was now chairman of the Roh Moo-hyun Foundation. Lee left the party in response. Kim's moves proved controversial, and many of his nominations for the party's proportional representation list were rejected by the rest of the party leadership, while favored candidates of Moon were ranked near the top of the approved list. Kim offered to resign in March, but decided to stay on as leader after a personal visit from Moon. Kim affirmed that he would continue to attempt to change the party's image, stating that the events had shown the party was "still unable to move on from its old ways".
Though losing votes to the People's Party formed by Ahn, Chun and Kim Han-gil—particularly in Honam—the party emerged as the overall winner of the election, garnering a plurality of seats (120 seats) in the National Assembly with a margin of one seat over the Saenuri Party. Lee Hae-chan returned to the Assembly as an independent representing Sejong City. Following its election victory, Kim Chong-in announced that the Minjoo Party would change its emphasis from welfare to economic growth and structural reform. Kim stated that the party would also change its position to support the establishment of for-profit hospitals, in contrast to the party's earlier opposition to the policy.
2017 presidential election victory
After the constitutional court impeached president Park Geun-hye over bribery, the Democratic Party's Moon Jae-in won the presidential election with a 41.1% plurality of the votes, with Hong Joon-pyo of Liberty Korea coming second with 24%.