Lukaku joined Everton on transfer deadline day in September of last year following an eye-catching campaign at West Brom.
During his time at The Hawthorns, Lukaku netted 17 Premier League goals from 35 appearances and was initially tipped to force his way into the Chelsea team, with his fellow forwards at Stamford Bridge misfiring.
Nevertheless, Jose Mourinho allowed the Belgium international to depart for another season and after scoring 15 times in 31 league outings – including one in Sunday’s 2-0 win at Hull City – Martinez believes that Chelsea can be "delighted" with how the move has worked out for all concerned.
"In any loan deal you do, all you want is for it to be a real success," he said. "I'm really pleased to say now that Romelu Lukaku has been a real success.
"I've seen him grow as a player, as a man and as a footballer and I think he has developed unique memories with Everton.
"I think you saw it today that the fans will always have great memories of Rom's footballing talent.
"Chelsea will be delighted with the progress of the player and we have benefited from having a player like Rom.
"Whatever happens next (for Lukaku) will always be positive and a part of what happens in the future."
England manager Roy Hodgson will announce his squad for the FIFA World Cup on Monday and a host of Everton players are in with a chance of selection following a season in which the club achieved a fifth-place finish.
Midfielder Ross Barkley and defender John Stones are two of the younger candidates and, although Martinez is unaware about whether either will be going to Brazil, he is certain they will be occupied in the post-season.
He added: "They will be busy, because as you know, they always have the opportunity to play for the senior side, but if not they will be with the Under-21s at the Toulon Tournament.
"In one way or another they will be busy. That was one of the reasons we had to look after them (and rest them against Hull), making sure they didn't go into the summer with a risk for an injury.
"They have been regenerating so are ready for whatever comes their way.
"(But) I don't know (which squad they will be in). Any manager you ask in the Premier League is going to be biased and say my players deserve to be in the national team.
"I'm not going to go down that route. I trust Roy's vision. I'm a big admirer of his experience and I'm sure whatever he does will be behind a plan and as a club we are happy to provide as many English talents as we can.
"Whatever the national team decides, we will be happy to help and will be very proud of our players representing their country."
