The deaths of the two-year-old girl and one-year-old boy in Chinese city Chongqing sent shock waves through the country in 2020.
Zhang Bo - the father of the children - and Ye Chengchen were previously found guilty of killing the two-year-old girl and one-year-old boy in 2020.
Zhang had begun an affair with Ye and later divorced his wife, and began conspiring to kill his children.
China's Supreme Court had called the couples' motives "extremely malicious", highlighting their "cruel methods".
The couple were executed in the south-western city of Chongqing on Wednesday. It is not clear how the execution was carried out, although death sentences in China are mostly carried out by lethal injection or a firing squad.
Zhang had begun an "inappropriate" relationship with Ye without informing her of his marital or parental status, but Ye continued to see him after knowing the truth, the court heard.
After Zhang divorced his wife in February 2020, Ye still saw the two children as "obstacles for her to get married to Zhang and burdens for their future life together".
Ye repeatedly pressured Zhang to carry out the murders, which they conspired to stage as an accidental fall, the court heard. On 2 November 2020, Zhang threw his kids out of the window of his apartment from the 15th floor.
News of their execution quickly began trending on Chinese social media site Weibo, drawing hundreds of millions of views.
"They totally deserve it for their crime," said one Weibo comment, liked more than 30 thousand times.
"Hope the kids only have peace and joy in their next life" another comment says.
Chen Meilin, the mother of the two children, said on Thursday night that "a nightmare that tortured our family for more than three years has finally disappeared".
The news came the same day as another high-profile execution - Wu Xieyu, an elite university student - who was found guilty of killing his mother by repeatedly striking her with a dumbbell in 2015.
-- Courtesy of BBC News