The former champions have not won a race since 2012 and finished last season, the first of a new partnership with Honda, ninth of the 10 teams with just 27 points compared to 703 for dominant Mercedes.
The three years without a win is the team's longest barren stretch since their absence from the top step of the podium in 1994-96.
"As we embark on the second year of our renewed McLaren-Honda partnership, all of us remain united in our purpose. That purpose is to develop our team towards our shared ambition: to win," said McLaren boss Ron Dennis.
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"We'll make no predictions as to when those wins will come," he added.
The new MP4-31 car was presented online in a predominantly black livery with some prominent new sponsors in LVMH's sparkling wine brand Chandon and watchmaker Richard Mille replacing the departed Tag Heuer.
The short-nosed car, described by the team as innovative, will make a first track appearance with Jenson Button at the wheel when testing starts at Barcelona's Circuit de Catalunya on Monday.
Last year was fraught with problems for McLaren, with the Honda engine lacking power and suffering from chronic unreliability.
The Japanese manufacturer has had to face mounting speculation already this year about the power unit, with some suggesting it has found dramatic gains over the winter and others reporting fresh reliability concerns.
"Learning from last year, we’ve made changes to the compressor and other hardware of the power unit during the break, maturing our overall concept," said Honda motorsport chief Yasuhisa Arai.
"We won’t know exactly where we stand until we reach the end of the two tests, but we’re looking forward to getting back on track, gathering data, and feeding back the information to our engineers so as to prepare for Melbourne and onwards."
The season starts in Australia on March 20.
Spaniard Fernando Alonso missed that race last year, suffering concussion after a testing crash in Barcelona, but the double world champion said he was excited and raring to go.
"The aero package shows fantastic attention to detail. The whole car is beautiful in fact...and I’m 100 percent ready for the challenge ahead," he said in a team release.
(Editing by Amlan Chakraborty)
