He will replace compatriot Fernando Alonso at the Woking team, where he will race alongside British rookie Lando Norris.
Sainz has had the majority of his career to date managed by Red Bull, bursting onto the scene with sister team Toro Rosso in 2015, before going on loan to Renault for the closing stages of 2017 and the full 2018 campaign.
Speaking to CRASH.net, Sainz spoke of how the McLaren move puts him in control of his own career for the first time in Formula 1.
“I’m really grateful for Red Bull, without Red Bull I wouldn’t be sitting here today as a McLaren driver,” Sainz explained.
“So I really need to be grateful for everything that they’ve done for me.
“But it is true that this is now a new chapter in my career, I am kind of managing myself in a way and I am independent.
“This independence comes with a two year contract with McLaren so something that I really wanted, [to] find my first two year deal with a team. If that team is McLaren even better!
“[I’m] looking forward to it,” he added. “I’m going to be a new Carlos and I’m really looking forward to this new chapter in my life.”
After finishing P6 in the 2018 Constructors’ Championship, McLaren are hopeful of climbing up the grid once more as they go in search of a first race win since 2012.
But, even with the additions of former Porsche LMP1 chief Andreas Seidl and former Toro Rosso technical chief James Key, Sainz warned the team not to get too far ahead of themselves, adding his new team will have to work “little by little” to find a way back up F1’s pecking order.