Alonso made his debut as a 19-year-old with Minardi in 2001 and has since claimed 32 victories in 236 races with this season representing his 14th in the sport, excluding the year he spent on the sidelines as a test driver for Renault.
"I think after 15 or 16 or 17 years in Formula One, whatever it will be, it's enough," Alonso told reporters at the Shanghai International Circuit on Thursday ahead of this weekend's Chinese Grand Prix.
"I will close the loop, I will close part of my life," he said, addressing a question about whether he would remain in the sport in some capacity once a driving career that brought him back-to-back world titles from 2005 ended.
"I started with a McLaren when I was three years old," he joked of a replica car bought for him by his father.
"I will finish with a McLaren but the real one in Formula One and that will be one-third of my life with a great experience, with great memories, with great friendships."
Widely regarded as the best driver of his generation, Alonso has often found himself in the wrong place at the wrong time.
He joined McLaren at the start of this year from Ferrari, returning to a team he had left following a single acrimonious season in 2007.
He then spent five frustrating seasons with the sport's most glamorous team from 2010, during which time he came close but failed to add to his world title tally.
BAD TIMING
The timing of his move to McLaren could also be questioned as the team are at the start of a new engine partnership with Japanese manufacturer Honda, who have struggled to come to terms with the sport's turbo-hybrid rules.
The combination that once dominated Formula One is now a regular fixture near the back of the field while Ferrari have returned to winning ways with Alonso's replacement Sebastian Vettel claiming victory at the Malaysian Grand Prix last month.
However, Alonso said that while he had enjoyed his time at Ferrari, he did not regret his move and felt inspired by the challenge of helping the eight-time constructors' champions return to the front of the pack.
"Five fantastic years, we've been very close two times to winning the championship and I only have good memories and good feelings," Alonso said of his time at Ferrari.
"But it was enough. To keep doing lap after lap, year after year, that was not anymore my motivation.
"It's challenging but I'm looking forward, starting in a new team, with a new project... This makes me happy and makes me full. I was not happy with my mind and my soul anymore."
(Editing by John O'Brien)
