The McLaren MCL35 was built for the 2020 season only but do the disruptions caused by the COVID-19 pandemic, its lifespan has been extended into 2021. The MCL35 made its racing debut in 2020 at the Austrian Grand Prix where it was driven by Carlos Sainz Jr. and Lando Norris. By the end of the season, McLaren was in third place in the World Constructors' Championship for the first time since 2012, with podium finishes at the Austrian and Italian Grand Prix.

Drivers for the 2021 McLaren team include Norris and Daniel Ricciardo, as Sainz switched to Ferrari.

In response to regulations for the 2021 season, including the reduction of the overall downforce of the car and a switch to the Mercedes Power unit (from the previous Renault power unit), the MCL35M received several substantial revisions, including the electronics, cooling, hydraulics, control boxes, and pipework for air and fluids. McLaren was the only team to change their car's architecture which meant the team was required to re-homologate their chassis. A new gearbox was introduced which McLaren developed independently. Due to the new gearbox, the car's wheelbase was extended. Additional changes were made to the rear end of the chassis and the gearbox housing.

Due to the pandemic, the 2021 season would be run under a token system, and since McLaren had agreed to a new engine supplier prior to the start of the pandemic, most of their available tokens were used to accommodate the switch in power units. Both engines were built to similar specifications, but are different in several areas. The Mercedes-AMG unit has a split turbo while the Renault system used a conventional turbocharger. The German-built system used a turbine positioned behind the engine and connected to a separate compression in front of the engine, located via a shaft, a configuration that accommodates a larger compressor.

Additional changes were made to the air intake of the MCL35M, with a more conventional design, and sidepods receiving a more sloping design to help circulate air onto the floor and into the diffuser to create more downforce. The inboard diffuser strakes are attached to the floor of the car, allowing the team to run a larger diffuser.

by Dan Vaughan