But Mr Annan stressed the need to prevent abuses or xenophobic reactions from native populations.
In a report to the General Assembly, he argued that "international migration, supported by the right policies, can be highly beneficial for the development both of the countries they come from and of those where they arrive."
He however warned in his "early road map for this new era of mobility" that these benefits were contingent "on the rights of the migrants themselves being respected and upheld."
The report pointed out that migrants last year numbered 191 million, including 115 million in the developed world, compared with 155 million in 1990.
Europe hosted 34 percent of the world's total in 2005, North America 23 percent, Asia 28 percent, Africa nine percent, Latin America and the Caribbean three percent, and three per cent to Australia and New Zealand.
Mr Annan submitted his report ahead of a high-level meeting on international migration and development which the General Assembly will host September 14 and 15.
The report was released at a time of heightened concern and social tensions in rich countries, particularly in North America and the European Union, in the face of an uncontrolled influx of illegal immigrants from poor countries.
The United States is considering sweeping immigration reform proposals, including building a huge border fence to stop illegal immigrants from Mexico.
The European Union is facing a similar influx of poor immigrants from Africa via the Spanish Canary Islands.
Benefits and problems
"We are in the midst of a new migration era and international migration today is indeed a global phenomenon," Mr Annan said.
"Large numbers of people migrate in search for a better life, not only between neighbouring countries or within a region, but to and from the uttermost ends of the earth," he said.
Pointing to accumulating evidence of the benefits unleashed by global migration, he said: "It is no coincidence...that many countries which not so long ago were primarily sources of migrants. For instance Ireland, several countries in southern Europe, the Republic of Korea and Chile, have developed spectacularly, and now boast thriving economies which make them an attractive destination for migrants."
Remittances sent home by migrants worldwide jumped from US$102 billion in 1995 to an estimated US$232 billion last year, the report said.
However, Mr Annan conceded that migration also brought its share of problems, including abuses of migrants by smugglers, traffickers and "unprincipled employers", and "xenophobic reactions" from native populations.
"The benefits that migrants bring to the country as a whole and over time, are often eclipsed by more immediate and local grievances, whether well-founded or not," he noted.
He said more and more governments were trying to channel the flow of migrants "whether out of or into their countries, in ways that maximise benefits while minimising the adverse side effects".