Bill Richardson, a former two-term Democratic governor of New Mexico and later U.S. ambassador to the United Nations has died. He was 75.

The Richardson Center for Global Engagement, which he founded, said in a statement Saturday that he died in his sleep at his home in Chatham, Massachusetts.

"Governor Richardson passed away peacefully in his sleep last night. He lived his entire life in the service of others — including both his time in government and his subsequent career helping to free people held hostage or wrongfully detained abroad. There was no person that Governor Richardson would not speak with if it held the promise of returning a person to freedom. The world has lost a champion for those held unjustly abroad and I have lost a mentor and a dear friend," said Mickey Bergman, vice president of the Richardson Center.

"Right now our focus is on supporting his family, including his wife Barbara of over 50 years, who was with him when he passed. We will share further information as it becomes available," he added. 

BRITTNEY GRINER'S RUSSIA DETENTION: WHAT BILL RICHARDSON'S INVOLVEMENT COULD MEAN FOR WNBA STAR

Richardson was a U.S. congressman and Secretary of Energy under President Bill Clinton in addition to his roles as governor and ambassador to the U.N. 

However, he is best known for his post-government career, in which he worked with his nonprofit foundation to free people held as political prisoners or hostages in foreign countries. 

Founded in 2011, the Richardson Center for Global Engagement has worked with more than 80 million families and provided them support and guidance while their loved ones were detained abroad. Richardson engaged in "fringe diplomacy" to bring foreign parties to the negotiating table and bring those detained back home, the center said.

NEW MEXICO AG VOWS TO PROCEED WITH EDUCATION LAWSUIT

Fox News Digital confirmed in May that Richardson was involved in freeing WNBA star Brittney Griner from Russian custody. Richardson previously helped secure the release of American journalist Danny Fenster from a Burmese prison in November.

Richardson's work earned him multiple nominations for the Nobel Peace Prize, including for this year. 

Sen. Ben Ray Luján, D-N.M., issued a statement calling Richardson a "giant in public service and government." 

NEW MEXICO TEEN ACCUSED OF KILLING NEWBORN FACES ‘NONSENSE’ PETITION TO BAN HER FROM COLLEGE: LAWYER

"In his post-government career, he was trusted to handle some of the most sensitive diplomatic crises, and he did so with great success. Here in New Mexico, we will always remember him as our Governor. He never stopped fighting for the state he called home," Luján said. 

"Governor Richardson was a close friend who held the same House seat that I was elected to. He knew how to get things done, and he worked closely with my late father in the Legislature.

"His passing is incredibly heartbreaking for so many New Mexicans who knew and respected him. He leaves behind a legacy that will never be matched, and one that New Mexicans will always take pride in. My prayers are with Barbara, the Richardson family, and all New Mexicans. His memory will always be a blessing."

The Associated Press contributed to this report.