The Japanese boy band, which sold 35m records up to last year, will disband on 31 December, its management agency said on Sunday.
Rumours of a split had been rife since the turn of the year, but had all previously been denied.
Its five members, who are aged between 39 and 43, are now expected to pursue solo careers.
The band, formed in 1988, has built up a huge fanbase in Japan and throughout Asia with members appearing frequently in films, soap operas, and commercials.
Members of SMAP, which stands for "Sports Music Assemble People", have also appeared on cookery shows and Japanese coverage of the Rio Olympics.
SMAP(全称Sports Music Assemble People“体育音乐人组合”)也同样出现在烹饪节目和日本转播里约奥运会的节目中。
Their popularity has even made them ambassadors for diplomatic relations between Japan, China and South Korea.
In 2011, they were the first Japanese pop group to visit China in a decade, amid a row between the countries over disputed territory. Their Beijing concert was attended by 40,000 people.
A statement by the group’s managers Johnny and Associates said they were "truly and deeply pained and sorry" to not be able to take part in 25th anniversary celebrations.