Jessie, 24, raised over £500,000 and is now getting used to her new look and has already done her first photo shoot.
"My first shoot with no hair! Kept touching my head lol what day night! So honoured to be a part of" she tweeted.
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Speaking to host Dermot O'Leary on the night, Jessie J said: "It's the weirdest feeling."
"It feels so liberating. But this isn't about this, it's about donating." The singer said it was "amazing" to have raised so much money, and added: "Everyone's crying. My mum's back there, crying with happiness."
Jessie joined some of the UK's biggest celebrities and presenters who took part in the fund-raising extravaganza for Red Nose Day's 25th anniversary.
Also using their famous faces to encourage the British public to donate to the charity that help thousands of people in the UK and Africa were Simon Cowell and David Walliams. The Britain's Got Talent judges were joined by Louis Walsh, Dermot O'Leary and Olly Murs for a humorous wedding sketch that saw music mogul Simon marry himself.
Pop music's hottest boy band One Direction performed their official Comic Relief single, a cover version of Blondie's One Way or Another. The boys, Niall Horan, Zayn Malik, Louis Tomlinson, Liam Payne and Harry Styles entered into the spirit of the occasion by sporting red items of clothing and red noses, with Louis even dying his hair red.
Some of TV's best-loved characters also returned to the small screen, including Ricky Gervais' David Brent, Dawn French's Vicar Of Dibley and the cast of Call The Midwife during the night hosted by Davina McCall, John Bishop, Jonathan Ross and Comic Relief co-founder Lenny Henry.
Amidst the evening's fun there were also harrowing reminders of what Red Nose Day and Comic Relief are about, with moving films on the effects of malaria, pneumonia and starvation in Africa and domestic abuse in the UK.