South Africa remains deeply divided racially despite the fall of apartheid more than two decades ago, with most of the black population continuing to live in poverty.
He faced chairman Wilmot James for the job, and was elected at a party conference in Port Elizabeth.
Maimane, 34, who begun his victory speech in his native Xhosa language, told delegates his priorities would be fighting for a fairer society with equal opportunities for all.
“We can transcend racial inequality, but this can only happen if every South African acknowledges the injustices of apartheid and if we all recognise that racial inequality of the past still remains with us today,” Maimane, who was born in the black township of Soweto in Johannesburg, said.
The Democratic Alliance’s (DA) leader of eight years, Helen Zille, 62, stepped down after leading the party to win 22 per cent of the vote in the 2014 national election, its best performance. Ruling party and former liberation movement African National Congress won that poll by more than 60 per cent.
Ms Zille, told The Citizen that she was relieved to be stepping down.
She said: “I will campaign for the DA, I will do what the new leadership would like me to do without trying to lead from the behind and interfering.”
She had suggested that a black leader was needed to be a viable opposition against the ruling African National Party.
DA’s position as the leading opposition party is challenged by hard-left Economic Freedom Fighters that won 6 per cent of national elections last year.
Maimane’s rise to prominence began in 2011, when he became the party’s national spokesman. Last year, he lost his bid to lead the provincial government of South Africa’s richest province, Gauteng, but shortly afterwards became his party’s parliamentary leader.