The move was part of a planned reshuffle of senior civil servants and ministers aimed at setting up a cross-party "neutral" cabinet and assuaging public anger with the president and her administration.
Park has been engulfed in a political storm over allegations that she allowed a long-time friend, who holds no political position, to meddle in affairs of state -- including cabinet appointments.
The friend, Choi Soon-Sil, is currently being questioned under emergency detention by prosecutors over her links to Park and other allegations of influence-peddling and fraud.
A presidential spokesman said Premier Hwang Kyo-Ahn had been replaced "in connection with the current situation" and added that the finance and public safety ministers were also being changed.
The new premier was named as Kim Byong-Joon, a former top aide to the late liberal president Roh Moo-Hyun.
The prime minister is a largely symbolic post in South Korea, where power is firmly concentrated in the presidency.
Suggestions that Choi Soon-Sil vetted presidential speeches and was given access to classified documents have exposed Park to public anger and ridicule and, with just over a year left in office, pushed her approval ratings off a cliff.
In an effort to deflect some of the criticism, Park has promised to create a neutral cabinet, bringing in members from outside her ruling conservative Saenuri Party.
