Posting a selfie on Instagram with Schwarzenegger, Pratt made the announcement in his caption.

"Katherine and I are so humbled and honoured to be joining Special Olympics as global ambassadors," he said.

"Come with us as we rocket the #InclusionRevolution to new heights!"

Pratt also praised Marvel Studios for vowing to hire a Special Olympics athlete to work on his upcoming film Guardians of the Galaxy 3, while urging more companies to follow suit.

This person will act as a paid production assistant on set.

"The studio’s partnership with the Special Olympics is an excellent step in showing the importance of diversity and celebrating the outstanding capability of those with intellectual disabilities," Pratt added.

"We are hoping Marvel is the first of many companies to take a stand and celebrate the inclusion of the intellectually disabled. 

"I am so pumped to start production and to continue to spread the message of love for those with special needs."

The 31-year-old Schwarzenegger, who is the oldest daughter of actor and former politician Arnold Schwarzenegger and journalist Maria Shriver, looks to continue on the legacy of her grandmother and Special Olympics founder Eunice Kennedy Shriver.

"Special Olympics has always been a huge part of my life," said Schwarzenegger.

"My grandmother dedicated her entire existence to being an advocate for those with special needs and my childhood consisted of going to Special Olympics international events and my cousins and I being camp councillors at Camp Shriver.

"Chris and I are so thrilled to be a part of the Special Olympics family as a couple and to continue to spread the mission of SO [Special Olympics] and advocate whenever and wherever we can about inclusion, dignity and acceptance."