Mallard's video shows the silverback coming just inches away from the camera, before brushing aside the Speaker, sending him back onto his butt.
The Speaker also posted images of his time in the rainforest, capturing footage of a mother silverback with her baby, and another gorilla hiding in the trees.
Kiwis took the opportunity to poke fun at Mallard, with one saying "gave you a sitting order, Mr Speaker."
"Very unparliamentary behaviour," another joked.
Rest day for delegation to Rwanda. Climbed into rain forest and was lucky to meet this wonderful family.
Posted by Speaker Trevor Mallard on Saturday, 20 April 2019
Mallard's cross-party Africa trip, designed to lay the groundwork for trade, was his own initiative and followed advice that New Zealand should establish more frequent relations with African countries.
"The advice when I first came to be Speaker from [former deputy prime minister and former foreign minister] Don McKinnon was that there are lots of places where New Zealand has links only when we want something.
"One of the roles of the Speaker can be to develop or reinforce links which otherwise would be very thin. There's no doubt in the longer term, because the GDP is increasing quite rapidly in a number of African countries, good contacts now make a lot of difference in 20 to 30 years as far as trade is concerned."
It will be New Zealand's first Speaker-led delegation to Ethiopia, where the African Union is based, and Rwanda.