MANILA — The former boxing champion Manny Pacquiao has shuffled his way into the presidential race in the Philippines.

Mr. Pacquiao, the country’s best-known athlete, already holds a seat in the Senate but faces tough opposition as a presidential candidate. He was formerly the president of the PDP-Laban, the ruling party in the Philippines, before being ousted by a faction loyal to President Rodrigo Duterte, whose government Mr. Pacquiao has accused of corruption.