The 36-year-old pop star revealed the news in a candid post on Instagram in which she explained she sought medical help after welcoming her first child - son Sky - last year "exposed" a lot of her symptoms.
Jessie wrote: "Hello. I was diagnosed with ADHD and OCD about three months ago. In telling people a lot of the reaction I got was, 'Yeah I mean we knew that' (which I'm sure some of you are doing right now) and of course I knew to some extent but having a baby has let's say ... exposed it a lot more, which was comforting in a way, as it made it feel less heavy and scary.
"But also in moments has made me feel like I can't talk about it. F*** that. Here I am talking about it."
Jessie went on to tell her followers she has felt " a little different" her whole life and her diagnosis has allowed her to rethink the way she deals with her personal and professional issues.
She wrote: "It's weird when you know you have been a little different and felt things differently your whole life, and finally one day when you least expect it, someone really explains why and you can't avoid it.
"ADHD has such a wide spectrum it's like a mystery putting your version of it together, that's how it's felt for me. In really understanding ways to cope, excel and grow with it. Tbh [to be honest] I low key feel like it's a superpower as long as you look at it from the right perspective and have the right support and people around you that can navigate it with you.
"It's made me re think about my whole life. The way I've been, the way I deal with things. The relationships I have had. How I work and how I love.
"It's empowered me and honestly sometimes has overwhelmed me all at the same time."
The 'Price Tag' star added that she feels happy to share her news with strangers on social media because there are so many other people going through similar issues and getting a diagnosis has allowed her to "love herself".
She concluded: " It has made me love myself even more. I'm hugging 11 year old me. Who would clean her trainers with a toothbrush when she was stressed and to this day has lived with a 1000 lists to not feel like life will crumble.
"Here's to getting to know yourself even more through life. And loving yourself all the way. Nothing in life defines us, but it helps us grow and become a more wholesome version of ourselves."
Jessie was supported by fellow pop star Becky Hill, who told the singer she was also went through a life-changing diagnosis last year.
Becky commented on the post: "I was diagnosed last year, think i'm also suspected autistic too, u should follow @adhd_love_ they're great at making you feel incredibly normal and able to laugh at and love our neurodivergent ways.
"One video said 'If i didn't have ADHD as a label, I'd come up with much worse ones of my own like lazy or disorganised'
"I've really learnt to love and have compassion for myself since the diagnosis. I also think you can't be an artist without being different from other people, it's what makes us special."