Emeli Sandé and Jess Mills will also feature at the EQUALS Live show held at London's Royal Festival Hall on March 9.
Lennox will host the event, which will aim to raise awareness towards gender equality as part of International Women's Day.
Speaking about the show, Lennox said: "I'm so proud to be hosting an evening of British female artists in celebration of International Women's Day. EQUALS Live at Southbank Centre will shine a spotlight on an incredible new generation of women in music who are raising their voices in solidarity with women across the globe.
"International Women's Day is the perfect time to reignite debate about what a more equal world would look like with a new generation and to finish the work of the women and men who paved the way before us."
Sinead O'Connor, Emmy the Great and Gaggle will also appear at the festival, which takes place between March 7 to March 11.
Katy B will perform at the Isle of Wight Festival this summer.
> Katy B teams up with Robbie Williams songwriter Guy Chambers for album
Watch the video for Katy B's 'Easy Please Me' below: