Free the Children has teamed up with Virgin Atlantic and Barclays to launch the charity project at Wembley Arena on Friday, March 7.
Harry Potter's Evanna Lynch, Glee star Jacob Artist, and singer Birdy will also make an appearance at the event.
Pretty Little Liars star Shay Mitchell, Sam and the Womp and vocal group The Tenors complete the latest lineup.
Ellie Goulding is to headline the environmental event, while there will also be appearances from Malala Yousafzai, former US Vice President Al Gore, and Clive Owen.
MTV's Laura Whitmore will host the event alongside Bluey Robinson and Lilah Parsons. The day will consist of educational speeches and performances in front of 12,000 students, teachers and supporters from over 400 schools.
We Day has already staged events in the US and Canada. Students can apply for tickets by completing at least one local and global charity act of their choice as part of Free the Children's We Act programme.
Jennifer Hudson said of the event: "We Day captures the very spirit that my sister and I continue to spread within our own organisation, the Julian D King Gift Foundation.
"It's that inspiration of the next generation that will bring change to this world. I've been a part of We Day in North America and the energy from these young people who come together to make a difference is simply contagious."
Birdy said: "I'm so excited to be part of the first ever We Day in the UK. I'm really proud to be part of an event that encourages people around the world to work together and to take action on social issues and promote positive change."