"This opportunity came as somewhat of a surprise, but I never did give up on my ambition and childhood dream to reach F1", Hartley said.
New Zealand's last F1 driver was Mike Thackwell who raced in 1984.
"Brendon is coming as the reigning 24 Hour Le Mans victor and he's also leading the current FIA LMP1 World Endurance Championship, which he won in 2015 as well".
Autosport magazine is reporting that 27-year-old Hartley is the favourite to replace Gasly for the race at the Circuit of Americas track and is in the frame to get a full-time drive at the team next year.
Hartley had to make do with a role as Red Bull reserve driver in 2009, a job he shared with Ricciardo, as he struggled for form in Formula Renault 3.5.
Toro Rosso team principal Franz Tost pointed out that Hartley had longstanding Red Bull roots, and also hinted that the team - which tends to try to promote young talents ready for promotion to the Red Bull team - was eyeing a more experience pair of hands to close out the season.
Hartley was not content with sticking around the F1 paddock as a reserve driver and began racing in endurance events in 2012 - the same year he joined Mercedes as a test driver. He also won the 2015 LMP 1 endurance championship.
Gasly will be racing in the Super Formula finale but is expected to return to action in Mexico; Hartley is believed to be a potential candidate for a 2018 seat with Porsche pulling out of the World Endurance Championship at the end of the year.
"He'd have to go to formula one because that has been his main aim from his early days, and what he has been aiming for", Smith said.
"I could see that when he was 12 years old driving Formula Vees, driving off the track and doing all sorts of insane things, he tried so hard - and Brendon never gave in". However, the rumor goes that Kvyat threatened to quit Formula One and Toro Rosso should he not get his seat back.
"He is a wonderful kid and It has been so good to associated with him over the years".