Mr Byrne, 29, severed the thumb on his left hand last December while sawing through a piece of wood.
Surgeons attempted in vain to reattach the thumb that was vital in Mr Byrne's job as a paver and plant operator and in his role as a father to his eight-year-old son.
Then to his surprise Umraz Khan, a plastic surgeon at Frenchay Hospital, said he would transplant the big toe from Mr Byrne's left foot on to his hand – and that is exactly what he did during an eight-hour operation.
Mr Byrne, of Fishponds, said: "Mr Khan re-attached my thumb but it had been badly damaged and although we tried everything – including leeches – to get the blood flowing again, it did not take.
Doctors explained to Mr Byrne that his thumb was the "dominant" digit and that while losing his toe may affect him in the short term, its use on his hand would far outweigh the loss to his foot.
Mr Byrne said: "Mr Khan said to me 'You will have a thumb even if I have to take your toe'.
"I thought he was joking, but he was serious and nine months later here it is.
"The aesthetics of it don't bother me, I am just happy that it works.
"My work as a paver would have been destroyed without the use of my hand because I couldn't pick up a brick without a thumb – but now I hope I can be back at work in a few months.
"I never thought it would work but the surgical teams and nurses have done such a fantastic job and the care has been amazing."
Mr Byrne will now have physiotherapy to help him to adapt to using his new thumb.
He even hopes that he will be able to be back playing rugby next year.
Frenchay Hospital is a regional micro-surgery centre and has an international reputation for results and outcomes for patients needing this sort of complex surgery.
Mr Khan led two teams of surgeons and anaesthetists – one working on Mr Byrne's toe while the other worked on his hand at the same time.
He said: "It is quite a rare thing to do and is a very complex micro-surgical procedure, which involves re-attaching the bone, nerves, arteries, tendons, ligaments and skin of the toe to the hand.
"James will have to learn to re-balance, without his left great toe, on to the ball of the foot but he will be able to walk and jog normally.
"The thumb is the dominant digit.
"Without it, James would not be able to do the things that we take for granted, like holding a pen or opening a door.
"It is still early days for him and he might need additional surgery to make it look more like a thumb.
"The loss of the great toe is not as disabling as losing a thumb, so the loss far outweighs the gain."
