The HTC-Highroad team leader became only the third German to win the Race to the Sun, which hardly deserved its nickname this year as the final stages were drowned in heavy showers and storms.
Martin finished ahead of compatriot Andreas Kloeden by 36 seconds, with Briton Bradley Wiggins third, 41 seconds adrift.
"It's so great. It's the biggest success ever in my career," the 25-year-old Martin said on the Promenade des Anglais at the end of the 124-km final stage won by French champion Thomas Voeckler.
The top three remained unchanged since Martin took the lead by winning Friday's sixth-stage individual time trial.
The last German to win the race was Kloeden, 11 years ago.
"It's a fantastic start to the season, which gives me so much confidence for the next races," said Martin.
"I'll be ready for the season. For sure my biggest goal is to have a good Tour de France. I hope I can do it. I think I'm ready for it." Martin, who was 36th in his first Tour two years ago and a lowly 137th last year, was helped by the weather on Sunday as none of his closest rivals dared to challenge him on the slippery descents to Nice.
Voeckler, regarded as one of the boldest riders in the bunch, attacked early with 10 others and was the only one left as he sped down toward Nice in reckless fashion with 10 kms to go, having dropped former junior world champion Diego Ulissi of Italy.
"I really took a lot of risks in the descents. I thought I was too old for such risks but I've still got it in me," said the 31-year-old Frenchman, winner of the fourth stage in Belleville.
Only 57 of the 175 riders at the start a week ago finished the race.
