The news of a donor comes eight days after Olsen's son, TJ, was placed on the transplant list.
"Today is a day of mixed emotions," Olsen wrote on Instagram. "A day we have prayed for has arrived. We were alerted last night that there was a donor match for TJ to receive his heart transplant.
"Walking our little boy, with tears of hope and fear in our eyes, was one of the toughest moments of our lives. We ask for everyone's prayers for TJ and his amazing team of doctors and nurses."
Later Friday, Olsen tweeted that TJ was out of surgery and expressed his condolences and gratitude to the donor family for their "selflessness."
UPDATE- TJ is finished with surgery and is being transferred to the ICU. We won't be able to see him for a few more hours but his doctors are very happy with the surgery. TJ will be sedated for a few days but his road to recovery has begun. https://t.co/JrYayw2j59— Greg Olsen (@gregolsen88) June 4, 2021
We also want to ask that everyone takes a second to pray for our donor family. Their selflessness during a tragic time gave our boy a chance at life. We don't know who they are, but we will forever be grateful for everyday we get to have with Tj— Greg Olsen (@gregolsen88) June 4, 2021
❤️ Olsen Family
In a Saturday afternoon update on Instagram, Olsen said that TJ was "resting comfortably" after the surgery and expressed his gratitude for his son's "incredible" team of doctors and nurses.
TJ was born in 2012 with a congenital heart defect that required four surgeries, including three open-heart procedures and the installation of a pacemaker.
"TJ has a long road ahead of him, but today is a huge step forward," Olsen wrote Friday. "From the bottom of our hearts, thank you for the outpouring of support through the journey."
Olsen and his wife, Kara, began the HEARTest Yard initiative shortly after the birth of TJ and his twin sister, Talbot, to raise money for less fortunate families going through crises like theirs.
The three-time Pro Bowl selection has donated millions to that charity and to the building of a 25,000-square-foot facility at Levine Children's Hospital in Charlotte known as the HEARTest Yard Congenital Heart Center.
TJ has been in the care of doctors at the facility since.
"We don't know how long we will be within these hospital walls," Olsen tweeted in May. "We do know that we are in full control of our attitudes and our outlook."
Prayers for TJ, from celebrities to people Olsen has never met, have flooded his timeline since the initial announcement. Olsen recently shared a photo from TJ's Little League team, which has been a large part of the family's support.