[5][6] Sainz Jr. and Norris replaced Fernando Alonso and Stoffel Vandoorne, both of whom left the team at the end of the 2018 championship.

The car was considered to be a big improvement compared to its disappointing predecessor, the MCL33,[9][10] often being the best of the rest in qualifying and race trim behind the three leading teams: Mercedes, Ferrari and Red Bull.

[15] The team recruited James Key from Scuderia Toro Rosso to oversee development of the MCL34 during the season.

[21] At the next round in Bahrain, both cars managed to get into the third part of qualifying for the first time since the 2017 Malaysian Grand Prix.

[23] On race day, Sainz made a good start, making the jump on Kevin Magnussen, and was contesting for P5.

However, Sainz would suffer front wing damage on lap 4 after making contact with Max Verstappen, and he had to pit as a result which dropped him to last place.

The race was worse for the team, as both cars would collide with Daniil Kvyat at turn 6 on the first lap, which dropped both of them to the last positions.

McLaren entered Spain with major upgrades to both cars, including revised barge boards, new engine cover, and a reshaped front wing, however both failed to reach Q3.

On race day, Sainz would lose out to Alexander Albon, falling to P10, but he would later execute a strong overtake, passing both Toro Rosso drivers on the outside line in turn 3 for P8.

During the race on Sunday, Sainz had an overheating brake duct due to a visor tearoff getting stuck in the disc.

Sainz was in ninth place when he was overtaken by Lance Stroll and Kvyat on the final stages of the race, falling to P11.

As for Norris, he had a strong performance, running comfortably in P7 up until the final lap, where he would suffer from hydraulic problems and gradually lose pace.

At the Austrian Grand Prix, McLaren began the weekend strong, finishing in the top 10 in every practice session.

In the race, Sainz displayed consistently fast pace and charged towards the front of the field to convert his P19 start into a P8 finish.

At the following round at the German Grand Prix, heavy amounts of rain riddled with the strategies and caused a chaotic race.

Sainz was caught out at turn 16 on lap 18, which caused him to run wide and aquaplane on the slippery drag strip area of the track before narrowly avoiding the barriers.

McLaren ended the first half of the season on a high in Hungary, with both cars getting into Q3 and scoring much-needed points.

At the start, Sainz managed to overtake Gasly and Norris, briefly threatening Sebastian Vettel on the entry of turn 2.

McLaren entered the summer break with a comfortable 82 to 43 point advantage over fifth placed Toro Rosso.

[24] After the summer break, at the Belgian Grand Prix, Sainz had a fifteen-place grid penalty for exceeding the quota for power unit components.

The mechanics had trouble with the rear jack, causing Sainz to be stationary in the pits for over 40 seconds, which resulted in him coming out over a lap behind the leaders.

Norris also collected debris from Charles Leclerc's earlier crash with Max Verstappen, causing him to pit to avoid a brake fire.

The race would also start well, with Norris and Sainz making up a place each after frontrunners Lewis Hamilton and Max Verstappen made contact at turn 2 on the opening lap.

In the United States Grand Prix, McLaren returned to form as Sainz and Norris qualified P7 and P8.

The Brazilian Grand Prix would start off as disappointing for McLaren as Sainz encountered engine problems during Q1, while Norris was eliminated in Q2.

In the race however, their fortunes would change entirely, as Sainz fought his way through the midfield (including Norris) on a risky one stop strategy.

After Ferrari teammates Charles Leclerc and Sebastian Vettel collided, punctured their wheels and retired, Sainz gained two positions and was now in P5.

Sainz's sixth place in the championship would be the first time since 2015 that a non-Mercedes, Ferrari, or Red Bull driver would finish higher than 7th in the standings.

The MCL34 featured the same iconic papaya orange livery with a blue triangular graphics on the engine cover.

At the Belgian Grand Prix, the team paid tribute to Anthoine Hubert with his logo on the airbox.