Henshaw earned his third international cap this month, coming on from the bench against the Wallabies in Ireland's second match of the GUINNESS Series.
At 19 years of age, the Athlone-born player made his Ireland debut against the USA in June and as part of the Summer tour of North America, he also played against Canada.
The former Westmeath minor footballer, who came through the rugby ranks at Buccaneers RFC, had already represented his country at Under-18, Under-19 and under-20 levels, and went on to play for the O2 Ireland Wolfhounds against England Saxons last January.
Before signing with the Academy under Nigel Carolan, Henshaw captained his school Marist College to the Connacht title in March 2012 - their first in 35 years.
While in his first year of the Academy, Henshaw was involved in Connacht's RaboDirect PRO12 opener against Cardiff Blues in September 2012. He took his chance well and established himself as a key component in the province's back-line.
He went on to play a further 22 matches in his first season, including all six pool games in the Heineken Cup, playing at both outside centre and full-back. To date, he has 30 Connacht caps to his name.
At the end of his first season, Henshaw was voted the Connacht Senior Player of the Year and also picked up the IRUPA Nevin Spence Young Player of the Year award.
This season Connacht head coach Pat Lam has favoured Henshaw in the centre, where he has played in all but three of the westerners' games.
Commenting on his new deal, Henshaw said: "I'm absolutely delighted to have signed a new contract with Connacht. Playing for Ireland recently was a huge honour and I was so proud to be representing my home province as well as my country.
"It's been an unbelievable 15 months and I'm so happy that I was given my first chance here at Connacht and can now continue to improve under Pat and the coaching team."
Lam added: "It's fantastic that Robbie has committed his future to Connacht Rugby. He is an extremely talented young man and is constantly improving as a player.
"I'm pleased that he sees Connacht as the place for him to continue that progress, playing week in and week out in big games.
"Robbie has proven himself to be one of the best young players in the country and I have no doubt that he will continue his remarkable career both with Connacht and Ireland."