The 28-year-old, who plays for Al Ain of Dubai, has not scored for the Super Eagles since October 2013.
“It was not an easy decision. I didn’t think my international career would come to a sudden end, but that is life,” Emenike told BBC Sport.
“Sometimes it’s better to remove yourself from an environment that doesn’t suit you mentally and physically, this is what I have done.”
He added: “I also felt it was important that people hear directly from me to avoid a funny twist to the story.
“I wish to thank the coaches who gave me a chance, fellow players and in particular big thanks to all my fans for their unconditional support.”
Emenike is the second player to announce his retirement from Nigeria’s senior squad this month, following Lille goalkeeper Vincent Enyeama – Nigeria’s most-capped player – who quit after a much publicised row with coach Sunday Oliseh.
Oliseh was reportedly considering leaving out Emenike for next month’s World Cup qualifier against Swaziland because he has not scored at international level for two years.
The former Spartak Moscow player, at Al Ain on loan from Turkish side Fenerbahce, has, however, featured in the first four matches since Oliseh took over from Steven Keshi.
Emenike made his international debut in a friendly against Sierra Leone in Lagos in February 2011 and was top scorer at the 2013 Africa Cup of Nations, helping Nigeria lift the trophy.
He made 37 appearances for the Super Eagles and scored nine goals.