During late 1948, the P.136 prototype performed its maiden flight; roughly six months later, it reportedly completed certification tests, clearing the type's entry into service.

During the late 1950s, a land-based utility aircraft, the Piaggio P.166, was developed from the P.136 and shares many design similarities, despite the deletion of the hull in favour of a conventional fuselage.

During the 1940s, barely a year following the end of the Second World War, Italian aircraft manufacturer Piaggio Aero, being keen to rebuild itself and its customer base in the post-war era, embarked upon the development of a new amphibian design.

Trecker secured the right to build complete aircraft, but he typically imported partially-constructed P.136s from Italy and assembled them with additional American-sourced components and systems.

[3] The Piaggio P.136 was a twin-engine pusher-type amphibian, being capable of carrying a maximum of five people with baggage, or a pair of stretchers and an accompanying medical attendant.

[1] While the general configuration and systems remained largely the same across different models, there were some customisations present in the cabin to suit its customer and intended purpose; while military aircraft would often be fitted with alternative instrumentation and radio sets, as well as additional transparent panels in locations like the doors for greater external visibility, civil P.136s would be furnished with more comfortable seating and additional panelling for sound exclusion and heat retention purposes.

[2] In terms of its controls and handling, Flight International observed that the P.136's boat hull makes little imposition on its flight characteristics: "As a landplane, it behaves as well as any comparable light twin, except that it pays the penalty of slightly lower cruising speed incurred by its marine capabilities"; the publication also praised its "excellent manoeuvrability" and ability to perform a "very steep approach".

As common amongst flying boats, both the control wheel and pedal travel are large, aiding in take-off runs to avoid water-based obstructions such as buoys.