Party secretary-general Lim Guan Eng announced this at a press conference at the DAP headquarters here.
He told reporters that Wong had been recommended by Selangor DAP leaders based on her solid work on the ground.
“She also assisted us in producing and directing our campaign materials for the Sarawak state election and the recent May 9 election.”
It was previously rumoured that former television presenter Yunna Tan was DAP’s top candidate to stand in the state seat.
However, party grassroots leaders reportedly disagreed with the choice of Tan.
The Balakong seat fell vacant after its assemblyman Eddie Ng died in a car crash last month.
The by-election will be held on Sept 8, along with another by-election for Seri Setia following the death of its assemblyman Sharuddin Baharuddin, who passed away on Aug 2 due to cancer.
Wong said she would continue Ng’s legacy through her efforts to improve the constituency.
“I will visit the voters there to get a better understanding of their needs.
“After all, we have over 20 days for campaigning,” she said.
She added that she would do her best and would not disappoint the voters in their support for DAP.