Sir Bernard Hogan-Howe told BBC London five cameras would be fitted in each van, three inside, one at the back and one at the front.
The move comes after he met the family of Sean Rigg, who died in police custody in Brixton during 2008.
One "gap" in video footage was around Mr Rigg's transport in a van, he said.
Sir Bernard said his relatives "were a sincere family who were obviously terribly bereaved because they had lost their brother".
He added: "They were concerned we didn't have full coverage by cameras of what had happened to their brother. There was some coverage but it was not complete."
The Met commissioner said the trend of increasing numbers of deaths across Britain in police custody - which at 17 such deaths in 2014-15, is the highest number for five years - was "certainly not true" in the capital.
The head of the Met added: "I am not complacent, any one of these deaths is a terrible thing for the family, but it is a relatively rare event in London.
"In Merseyside we had cameras in police vans for years and in the Met we did not do that and I made a promise we would do that."
Andrew Allison, at The Freedom Association, said he wanted to know why cameras would not be installed in all police vans as it "happened in one so it could happen in any" of the vans.
"What is going to happen to the tape? Will it be immediately erased? Who will have access to it?", he added.
Last month it was announced Met Police officers would wear cameras from March 2016.
The Met Police will introduce cameras into 135 prison transfer vans to increase transparency, Britain's most senior police officer said.