Hamilton's move to the German marque was confirmed last week with the Briton replacing seven-time champion Michael Schumacher, who today announced his second retirement from the sport.
Hamilton was reticent to talk about the reasons for his decision to leave McLaren after 14 years with the international media, having already held a press briefing with British journalists at the Conrad Hotel in Tokyo on Wednesday.
When questioned, he replied: "I'm not really here to talk about that this weekend. I'm here to talk about trying to win this World Championship still.
"We've got six races ahead in a great team that I've had a great, incredible journey with and I'm working on trying to finish that on a high."
But when asked if he felt more relaxed having made up his mind over where he will drive next year, Hamilton was more forthcoming.
He said: "Absolutely, yeah I feel fantastic. I am very, very happy and excited and grateful that I can now just focus on these next six races.
"I know there's a lot of work ahead of me and I know I'm leaving a very good car behind for Sergio (Perez)."
Hamilton has spoken with relish of the challenge he will face at Mercedes, a task made more difficult by the stature of the man he is replacing.
Even though Schumacher's second spell in F1 following his 2010 comeback has been a disappointment, Hamilton is fully aware of how difficult it will be to replace a man with seven world titles and 91 race wins to his name.
"I don't see myself as replacing Michael. I don't think anyone can replace Michael, he's a legend in the sport, he has achieved so much already," he said.
"I feel privileged to have been in F1 at the same time as him.
"I watched him winning all his world championships at home in my living room so to have been on the track with him in 2006, and then for him to come back and for me to get to race against him, has been a real privilege.
"I hope one day I can achieve some of the things he has done."
With his 2013 switch signed, sealed and delivered, Hamilton has turned his attentions to getting his 2012 title tilt back on track.
The 2008 world champion retired while leading in Singapore last time out and fell 52 points adrift of Championship leader Fernando Alonso with six races remaining.
Hamilton has never won at Suzuka but, with McLaren having the car to beat at the last four races, is hopeful of adding victory here to his CV.
"I love coming here," he said. "The whole trip has been fantastic so far and the track is one of the best tracks in the world.
"It is not one that I have won at before but I think we have a car to win and hopefully it's a better weekend."
His team-mate Jenson Button, meanwhile, faces an uphill struggle as he will have to take a five-place grid penalty this weekend after his gearbox was found to have the same fault that curtailed Hamilton's race under the Singapore lights.
Button is now a huge 75 points adrift of Alonso and a poor result this weekend could effectively end his hopes of repeating his 2009 success.
But while he watched team-mate Hamilton fend off questions about his future, Button is delighted he is staying put.
"It's nice not to be the one in that position - it normally is me," he said.
"We all move about. That's the way Formula One is. You're either trying to find a better possibility, a better team that you think can give you an opportunity to win races or you're looking for another challenge.
"There's always going to be people moving around in Formula One. It's the same with team personnel; it's not just the drivers.
"It just seems that it's all come at once."