Originally submitted to the Air Ministry as a four-engined high-wing monoplane weighing roughly 16,500 lb, the concept was well received by the Brabazon Committee, with Miles being issued with instructions to proceed.

While development proceeded, various agencies argued over the aircraft's specification, leading to multiple attempts to change the design midway though, delaying progress and inflating costs.

However, the lack of commercial involvement in the specification to which the aircraft was built likely heavily contributed to the lukewarm response it received from such operators, with British European Airways (BEA) opting to not introduce the type despite buying seven of them with intentions of doing so.

The origins of the Marathon are closely associated with the opportunities offered by the Brabazon Committee, which sought to best direct the British aircraft industry's efforts for the postwar civilian market.

Work on the project had commenced under Miles Aircraft Limited, having been originally envisioned as a four-engined low-wing cantilever monoplane that was had been intended as a natural successor to the prewar de Havilland Express.

It was decided to compromise on a four-engined aircraft with a high-mounted wing that weighed roughly 16,500 lb; this proposal was submitted to the Air Ministry for review, resulting in Specification 18/44 being written to fit it.

As per the convention at the time, development and ordering were overseen by the Air Ministry alone, with Miles being forbidden from directly communicating with commercial operators to seek input on their requirements or suggestions.

Around this latter stage of development, work was protracted by a multitude of state agencies becoming involved and pushing for their own diverse requirements to be incorporated, some of which were contradictory and occasionally impractical to achieve, such as the use of a pressurised cabin or a very high level of structural strength.

[8] However, on 10 May 1948, tragedy struck when one of the prototypes was lost during official trials held at RAF Boscombe Down; the loss was attributed to pilot error, having failed to adjust the fins to their normal position, resulting in mid-flight structural failure.

[9] The majority of excess aircraft were diverted for use by the Royal Air Force as navigation trainers, receiving the designation Marathon T.11 along with numerous internal modifications to suit the role.

No surviving airframes are known to exist but the upper fuselage section of Marathon M.60 G-AMGW was stored at Woodley, United Kingdom as part of the Miles Collection c. 2000[18] Data from British Civil Aircraft since 1919: Volume 2.