Speakman says it has been a "truly humbling experience" to work alongside "so many talented people" and described Sunderland's fans as the club's "greatest asset".
Speakman's Sunderland exit was confirmed on Friday morning, with the 46-year-old leaving after just over five years at the club. During his time at the Stadium of Light, Speakman guided Sunderland from League One back to the Premier League, with the Black Cats winning at Wembley on three occasions.
RECOMMENDED READING:
Speaking for the first time after his exit, Speakman has taken to social media and wrote on X: "The opportunity to be sporting director and lead this historic club over the last five plus years has been the honour of a lifetime.
"I owe a debt of gratitude to my wife and children for allowing me to live this experience and on so many occasions place the club before home.
"I was once told to 'work where it matters' and I've learned over these six seasons how much this club matters to the people of Sunderland. Re-establishing a team built on the region's identity, creating a deep connection with its people is an aspect I'll be most proud of.
"The same community welcomed our family and for that we'll be forever grateful to the many friends, neighbours, coaches and staff that made Sunderland our home - it's been a truly humbling experience to work alongside so many talented people.
"To all the players and staff past and present, thank you for believing in our shared vision.
"Ultimately all our success over these six seasons has been down to your unwavering commitment, technical excellence and attitude to deliver your best every day. For this you should all be immensely proud of where the club sits today.
"The greatest asset this club has are its fans and it's been a pleasure sharing some incredible memories with you all. Good luck for the remaining games this season."