He played a leading role in the investigation into the 2013 South Korean sabotage plot, which led to the conviction of Lee Seok-ki and the dissolution of the Unified Progressive Party.

[1] In May 2015, he was nominated by President Park Geun-hye for the position of Prime Minister of South Korea and assumed office on 18 June 2015.

Hwang assumed the role of Acting President of Korea in accordance with the presidential order of succession until the election of Moon Jae-in on 9 May 2017.

On 10 March 2021, Hwang announced his candidacy for nominee of the People Power Party in the 2022 South Korean presidential election.

He spent 30 years as a prosecutor, specializing in enforcing public safety and national security laws under the military junta of Chun Doo-hwan, gaining particular notoriety for targeting democracy activists by linking them with North Korea.

[7] In that role, Hwang played a key role in the Constitutional Court case against the left-wing Unified Progressive Party (which was accused of holding pro-North Korean views); the case culminated in a controversial December 2014 order banning the party, a decision that some saw as a blow to freedom of speech in South Korea.

[7][8] On 21 May 2015, Park named Hwang as Prime Minister of South Korea, following the resignation of Lee Wan-koo due to allegations of bribery.

[13] On 10 March 2017, South Korea's Constitutional Court upheld the decision to impeach President Park Geun-hye and removed her from office.

"[15] Hwang decided against contesting the South Korean 2017 presidential election, declaring it would be inappropriate to run, opting instead to focus on his position as Acting President.

In the 2020 legislative elections on 15 April, Hwang ran for the seat for the Jongno district of Seoul, which includes the Blue House and Gwanghwamun Plaza.

[25][26] On 5 February 2025, Hwang joined the legal team of impeached president Yoon Suk Yeol defending him from criminal charges relating to his declaration of martial law in December 2024.