Bradley Manning's letter, entitled The Next Stage of My Life, was signed with a handwritten signature in the name of Chelsea Manning.
The letter was broadcast on NBC's Today show as Manning's lawyer revealed the soldier's desire to live life as a woman.
More top news
Police appeal for information after father and two young children go missing from Kent home.
A father has been sentenced to life in prison after being convicted of intentionally leaving his toddler son to die in a hot car.
Theresa May has refused to rule out paying money to the EU after we leave, so that UK firms can still trade with the single market.