After a narrow loss to Pakistan in their opening game in Colombo, the Dutch bounced back in Delhi.
Chasing 157, De Leede, who had already taken two key wickets, remained unbeaten on 72 from 48 balls to guide the team to a commanding victory.
The win marked the Netherlands’ largest margin of success in T20 World Cup history, and De Leede became the first Dutch player to score a half-century and take two wickets in the same World Cup match.
Sent in to bat, Namibia reached 60-1 after nine overs before Logan van Beek removed Jan Frylinck for 30. De Leede then dismissed captain Gerhard Erasmus (18) and JJ Smit (22), while Nicol Loftie-Eaton fell for 42 from 38 balls, leaving Namibia on 156-8.
The Netherlands lost opener Max O'Dowd early, but a 70-run third-wicket partnership with Colin Ackermann steadied the chase. Ackermann fell for 32, but De Leede’s 72* featuring five fours and four sixes sealed the win.
The Netherlands take on the United States on Friday, while Namibia face defending champions India on Thursday.
The Pakistan government has given it's approval for their national team to take the field and play India in their T20 World Cup encounter, scheduled for Colombo on 15 February.
The International Cricket Council (ICC) has concluded that Bangladesh will not be sanctioned for refusing to play T20 World Cup matches in India.
Aiden Markram was in the runs while Lungi Ngidi took four wickets as the Proteas kicked off their T20 World Cup campaign with a 57-run victory against Canada in Ahmedabad.
Zimbabwe's fast bowling trio of Richard Ngarava, Blessing Muzarabani and Brad Evans shared nine wickets to set up an eight-wicket win against Oman in their T20 World Cup clash in Colombo.
