Hwang Kyo-Ahn, 58, was named as the new prime minister after his predecessor, Lee Wan-Koo, was implicated in a major bribery scandal and forced to quit in April after serving only two months.
As a former prosecutor and with two years under his belt as justice minister, Hwang was deemed fit to follow through on Park's pledge of an anti-corruption drive, presidential press secretary Kim Sung-Woo told reporters.
"We believe he is the right person to root out corruption prevalent in our society and carry out political reform to build a new Korea," Kim said.
The prime minister is a largely symbolic post in South Korea, where power is concentrated in the presidency.
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Under Park, it has proved to be a job that is both difficult to secure and equally tough to hold on to.
The president's first ever nominee withdrew after allegations about his past, and her initial prime minister was Chung Hong-Won, who then resigned after the April 2014 Sewol ferry disaster.
Two successive Park nominees to replace Chung withdrew their candidacies - again because of allegations of past wrongdoing - and the job finally went to Lee, who then stepped down last month.
The main opposition New Politics Alliance for Democracy described Hwang's nomination as "very disappointing", saying the justice ministry's political independence had been weakened on his watch.