In a statement published on the Tigers' official website, Mason offered thanks an gratitude to all those who have supported him throughout his career, from his family to various coaches, as well as those who have helped him recover from his life threatening injury.
"I am and always will be eternally grateful for the incredible network of people around me who have helped me to recover from what was a life-threatening injury in January 2017," Mason said.
"Thank you to my amazing fiancé, Rachel, who has been by my side and lived every single day with me since the injury, helping to give me the strength I've needed no matter how tough things got. We are so lucky to have now become the proud parents of our perfect baby boy George.
"To my Mum, Dad, sisters, and all of my family and close friends, thank you for everything. Despite how tough it's been and the challenges I've faced along the way you've all been there supporting me and words will never truly do justice to how grateful I am for your love and support."
Mason extended his thanks to Dr Mark Waller and Hull's medical staff, as well as the chairman and board for "being so patient with my recovery and sticking by me."
On boyhood club Spurs he said, "There are too many names to mention when it comes to talking about Tottenham Hotspur but I would like to say a special thank you to John McDermott, the Gaffer and everybody at Spurs for helping me to achieve my dreams.
"I am so proud to have come through the ranks to play for my club, the club I love. To have had the honour of captaining the team fills me with immense pride. Thank you to all of my teammates over the years, there are too many to mention, it's been a privilege to play alongside you all."
Mason made his England debut in2015, an honour "nobody can ever take away from me".
He added, "I feel content knowing that I dedicated my life to be able to play football at the highest level, hard work really does pay off! I love the game, I always will and I am excited to see where football will take me next."