Hamilton's 14-year working relationship with McLaren will come to an end at the conclusion of the season, with the Briton moving to Mercedes in place of Michael Schumacher, who announced his retirement on Thursday.
Many have questioned the wisdom of Hamilton's move from a team with winning pedigree to one with just one victory over the last three seasons.
But Ferrari's championship leader Alonso, who endured a torrid year as Hamilton's team-mate at McLaren in 2007, believes a change of scenery will be good for the British driver.
He said: "I think it's normal, it's just steps on your career. I said when the rumours were there that for Lewis I think it's a good thing to move on.
"From McLaren, (Alain) Prost was going out, (Ayrton) Senna, then it was me, now it's Lewis. And normally for a better life. For a good change.
"McLaren have not won the constructors' championship for 14 years and most of these years sometimes with the best car. I am sure Lewis wants to win as well."
Hamilton has been quick to play down his hopes of challenging for the title in 2013, but Alonso is in no doubt the 2008 world champion will once again be one of his main rivals.
When asked if he expected a Hamilton title tilt with Mercedes, Alonso said: "I think so, I think he did great in McLaren. He won one world championship, which is the target for all of us.
"He won races, he is considered one of the best drivers and for next year I think he will enjoy more and be very competitive.
"From next year I think he is a clear contender for the championship with Mercedes. They are a top team and with Ross Brawn there and with all the potential of a big company behind they are very strong."
Hamilton's switch means he will partner his former go-karting team-mate Nico Rosberg.
And Rosberg sees no reason why the pair should not work well together, but made it clear he does not fear Hamilton's arrival at the Brackley-based team.
Rosberg said: "At the moment I have a seven-time champion as my team-mate so the competition I have is very high.
"I think it will be a difficult challenge, it has been a good challenge over the last three years with Michael and I am looking forward to the challenge with Lewis.
"I remember him in go-karts, he is tough opposition for sure, he is one of the best out there at the moment. It will be good and it's great he is joining the team."
He added: "I don't see it as a defining season. Every season is important in F1 and next year will be important too.
"I am confident I will do a good job, and confident I will do well and push hard to do well. How I compare with my team-mate remains to be seen. I am not worried or anything as such."