The former Voice UK judge stars on the uptempo anthem alongside Ariana Grande and Nicki Minaj, and it was a momentous occasion, as it marks Jessie's first Number One in three years.
Taking to Instagram, she said: "Ladies we did it! THANK YOU for being so unbelievably amazing! For holding my hand on this part of my journey! I love you both and am so happy for us to share this moment. Number one in the UK BABY! @nickiminaj @arianagrande."
Draped in black lace, Jessie celebrated her success early while performing at London's G-A-Y nightclub over the weekend, where she was presented with a personalised cake.
It doesn't look like the party will stop anytime soon either, as Jessie says she plans on celebrating "every minute of it".
Speaking to the Official UK Charts Company, Jessie said: "I want to say thank you, thank you, thank you for making me number one. 'Bang Bang' is the first single off my new album Sweet Talker and for it to be such a success around the world means so much to me.
"To be number one for in the UK for the first time in three years… I'm going to celebrate every minute of it, I might even go bowling!"
Sharing another photo on Instagram in the early hours of this morning (29 September), an ecstatic Jessie said: "So happy! Thank you for your endless love support and belief."
'Bang Bang' has already achieved huge success all over the globe, entering the top 10 charts in America, Australia and across Europe. The single is the lead from Jessie's new album Sweet Talker and it is her third number one single since 'Domino'.
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Watch Jessie J, Ariana Grande and Nicki Minaj's video for 'Bang Bang' below: