Hydrogen fuel-cell power has been tried out successfully in limousines, trucks and buses, but load-luggers like the Hilux are still largely powered by beefy diesel engines.
Toyota's UK offshoot in Derby said customers in remote areas were looking for a compatible green vehicle which could be refuelled as quickly as a diesel with no need for electric recharging.
The project backed by various consortium partners is supported by UK government funding.
The new pick-up looks no different from a regular 2.4-litre diesel Hilux, but under the bonnet is a fuel cell stack sourced from the Mirai car introduced in 2014.
The Hilux has been around in various guises since 1968 and is now in its eighth version.
In Toyota's latest version, hydrogen is stored in three high-pressure fuel tanks, giving the prototype Hilux an expected driving range of more than 600km. This is significantly further than might be achieved with a battery electric system.
The hybrid battery, which stores electricity produced on-board by the fuel cell, is positioned in the rear load deck, avoiding loss of cabin space. When driven, the fuel cell produces no tailpipe emissions other than pure water.
Behind the cab bulkhead is a reinforced metal box containing a battery about the same size as that in a hybrid car. The first of 10 hydrogen Hilux prototypes that will be built by the end of this year, says Toyota. No date for a production model has been given.