"There has been for several months a consistent and coordinated attempt to undermine my leadership and ensure that either this project failed, or I failed.
"This extended to the smear campaign that was run on the front pages of an Afrikaans weekly paper in an attempt to destroy my name and my integrity.
"This cowardly behaviour has put my wife and two young children in great danger as pictures of our home were published in the media," he said.
Maimane added that "despite my best efforts, the DA is not the vehicle best suited to take forward the vision of building One South Africa for All".
"It is with great sadness that in order to continue the fight for this vision I so strongly believe in, and the country I so dearly love, I today tender my resignation as leader of the Democratic Alliance.
"I will continue in the role as parliamentary leader until the end of the year, after which the party will go to Congress to elect new leadership."