De Lille has named her party Good.
Her new party will contest next year’s general elections in all nine provinces.
De Lille resigned as both mayor and Democratic Alliance member at the end of October, following disputes with the party.
“It’s time for all the good people in South Africa to unite and take action for the good of our country,” said De Lille.
“We are calling to action every single South African from all walks of life to join our movement today.”