In the opening game of a tri-series also featuring the Netherlands, Jan Nicol Loftie-Eaton smashed 11 fours and eight sixes before being dismissed for 101 from 36 deliveries.
The previous record was held by Nepal’s Kushal Malla, who reached a T20I hundred from 34 balls against Mongolia last year.
Namibia posted 206-4 batting first, before Jan Nicol Loftie-Eaton also took two wickets as hosts Nepal fell short in their chase, losing by 20 runs.
The three teams competing in the tri-series have all qualified for the T20 World Cup to be held in June in the Caribbean and United States.