The 62-year-old Belgian takes over the responsibilities of Juergen Stark, who resigned.
Praet has served on the six-member ECB executive board since June. His responsibilities have included human resources, budget and payment systems.
There had been speculation that responsibility for the ECB's economics department would fall to new board member Joerg Asmussen, who was named after Stark quit, or Benoit Coeure. Both joined the bank's leadership on Jan. 1.