Ramon Lopez said 6,000 jobs would be created in the Philippines as a result of the 13 agreements signed between private companies at the weekend, which covered areas such as health, defence and tourism.
"The private firms in Qatar have shown great interest in various projects (in the) Philippines," Lopez told the Qatar Tribune newspaper.
"There are many more opportunities where they can invest."
His comments came as Duterte prepared to meet senior government officials in Doha on Sunday, and less than 24 hours after the controversial former mayor addressed an adoring crowd of almost 7,000 supporters in Qatar.
More From This Section
During an hour-long speech, Duterte spoke also about his pledges on clamping down on corruption and sang a duet with a local Filipino singer, Hanna Uddin.
Some 240,000 Filipinos live in Qatar, and a large majority voted for the president in last year's election.
Despite criticism of the way some Filipino workers are treated in the Gulf, Duterte said earlier on his visit that expats managed to send home more than USD 7 billion (6.6 billion euros) in remittances in 2016.