The 31-year-old is one of five players, alongside Conor Murray, Cian Healy, Iain Henderson and Peter O'Mahony, to have won five Six Nations titles with Ireland.
Henshaw has won 77 Ireland caps since making his debut against the USA in 2013, scoring 10 tries.
He started all three Tests for the British and Irish Lions on their 2021 tour to South Africa.
"Even though we have enjoyed some success in recent years, there is great hunger within Irish Rugby to continue driving forward," said Henshaw.
"I believe that my best days are to come and I am excited to continue my journey here in Ireland."
IRFU performance director David Humphreys said: "Since breaking into the senior international squad 11 years ago, Robbie has been a consistent presence in one of the most competitive areas of the Irish backline. Robbie is a consummate professional and a popular figure who continues to set the bar high."
