The left-back joined the club at the age of six and rose through the ranks to the first-team where he made his debut in 2015 under Louis van Gaal.
The 23-year-old opened up about the highs and lows he experienced at Old Trafford during his long association with the club.
Borthwick-Jackson wrote on Instagram : "After 17 years at the club, it's time for me to leave Manchester United.
"Growing up as kid from Manchester, all I wanted to do was play for United.
"To make my debut for the club I grew up supporting was a dream come true and a day that will stay in my heart forever.
"I've had some great experiences, made some great friends and had the opportunity to play with/against great players.
"To that I owe a huge amount of gratitude to those members of the club who believed in me.
"Likewise I've had many negative experiences which in turn have become lessons, especially in recent years.
"It's revealed some truths in football most people won't ever see (in due time).
"Lastly I'd like to say a big thank you to all the fans who have support me and those who still continued to do so. I appreciate you.
"I'm looking forward to a new chapter that awaits me, wherever it may be."
Borthwick-Jackson joined the club in 2003 and made his debut against West Brom in 2015.
He made just 14 total appearances, though, and went on several loan spells in recent seasons.
The defender had temporary spells at Wolves, Leeds, Scunthorpe, Tranmere and most recently Oldham.
Cameron Borthwick-Jackson penned a farewell note to Manchester United following his release by the club.