The execution of Kim Jong Un's uncle, Jang Song Thaek is the biggest upheaval in North Korea since the death of Kim Jong Il.
The official newspaper of the party published a photograph of Jang in handcuffs and being held by uniformed guards, supposedly while on trial.
The state news agency said Jang was executed after being found guilty of treason.
An expert believes the move was done to further cement Kim Jong Un's hold on power.
North Korean politics are a mystery, and some in South Korea believe the reason behind Jang's execution could be a falling out between him and his nephew, which needed to be controlled.
South Korea and the U.S. both said they are closely following the developments.