The 25-year-old, who is now trying to live with the condition, says he's slightly relieved that it wasn't a 'degenerative disease' when doctors informed him of the news.
The 'Someone You Loved' singer also revealed he has Botox injections to try to control it.
Capaldi said on Instagram live: "I have been diagnosed with Tourette’s.
"I wanted to speak about it because I didn’t want people to think I was taking cocaine or something.
"My shoulder twitches when I am excited, happy, nervous or stressed. It is something I am living with. It is not as bad as it looks."
He added: "It’s a new thing. I haven’t really learnt much about it.
"I got Botox in my shoulder to stop it moving but I'm learning new ways to cope all the time. Some days it’s more painful than others, sometimes it’s quite uncomfortable but I guess that’s it.
"When they told me, ‘We think you’ve got Tourette’s’, I was like, ‘Do you know what, that makes so much sense’.
"When I look back at my interviews from 2018 I can see that I’m doing it."
Capaldi admits that 'it comes and goes' and that it isn't something he deals with regularly, explaining: "Sometimes I can go months without doing it. I thought I had some horrible degenerative disease so I’ll take Tourette’s."
According to the NHS, Tourette's syndrome is a 'condition that causes a person to make involuntary sounds and movements called tics'.
"It usually starts during childhood, but the tics and other symptoms usually improve after several years and sometimes go away completely.
"There's no cure for Tourette's syndrome, but treatment can help manage symptoms.
"People with Tourette's syndrome may also have obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD) or learning difficulties."
Examples of physical tics can include:
- eye rolling
- shoulder shrugging
- jerking of the head or limbs
- touching objects and other people
Examples of vocal tics include:
- throat clearing
- tongue clicking
- animal sounds
- saying random words and phrases
- repeating a sound, word or phrase
"Swearing is rare and only affects about 1 in 10 people with Tourette's syndrome," the NHS added.
"Tics are not usually harmful to a person's overall health, but physical tics, such as jerking of the head, can be painful."