Reddit, one of the most highly trafficked websites in the world, is replacing its interim chief executive, Ellen Pao, ending an eight-month tenure that was enmeshed in controversy.

Ms. Pao is resigning and being replaced by co-founder and former chief, Steve Huffman, the company said. He will rejoin Reddit’s other co-founder, Alexis Ohanian, who has returned to the company’s San Francisco headquarters full-time.

The...