The duo made their senior Ireland debuts on the summer tour to North America and Henshaw has since been included in the squad for the recent autumn internationals, during which time he came off the bench in the game against Australia at the Aviva Stadium.
Henshaw is regarded as one of Ireland's greatest talents, having been voted Connacht's Senior Player of the Year and also picked up the Irish Rugby Football Union's Nevin Spence Young Player of the Year Award at the end of his first professional campaign last season.
He played in all six of Connacht's Heineken Cup ties last term and wore senior club colours on 22 occasions in all, starting in both the No13 and No15 shirt to equal effect. He has added a further eight appearances to his name this season, including both European fixtures, and Connacht boss Pat Lam is convinced the 20-year-old has a bright future ahead of him.
"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," said Lam, who has already seen Kieran Marmion, Willie Faloon, Craig Ronaldson and Matt Healy extend their contracts at the Sportsground.
"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, week out in big games."
As for O'Donnell, the 26-year-old flanker is held in equally high regard at Munster having made huge strides over the past two seasons. After making his domestic debut as far back as 2007, O'Donnell has risen to greater prominence after finally earning his Heineken Cup spurs in December 2011. A stellar season followed last time out as he was named Munster Rugby Player of the Year in 2012/13, with a brace of Ireland caps coming in the summer as a result of his fine form.
He is currently sidelined with a knee injury he suffered against Zebre in September but both he and Munster coach Rob Penney are confident he will be back to his best when he returns to full training next month.
"This is where I want to be and I enjoy playing my rugby here. I know it hasn't been the best of starts to the season for me with injury but, like last year, I just want to come back fighting and push on to the next level again," said O'Donnell.
"Tommy is a great dynamic player and a huge asset to any side so we are particularly pleased that he has committed to Munster for another two years," added Penney, who has welcomed Keith Earls (knee), Ian Keatley (hip/groin) and Luke O'Dea (hamstring) back to training this week.
Both Munster and Connacht won one and lost one of their opening two European encounters, with Connacht narrowly missing out at home to Saracens before beating Zebre, while Munster slipped to defeat at Edinburgh prior to toppling Gloucester.
Next up for Munster is the double header with French giants Perpignan, while for Connacht comes the prospect of an arguably even bigger challenge against four-times Heineken Cup kings Toulouse.