The 21-year-old lock forward joined Exiles in 2009 but had his early development disrupted by injuries.
This season, however, he has made 12 appearances and Irish director of rugby Brian Smith has no doubt he will continue to improve.
He said: "Kieran Low is one of the most naturally gifted players I've worked with. He's a big fella with excellent skills and plenty of desire.
"Kieran is developing his set piece play very well under Glenn Delaney and it won't be long before he commands a starting spot in our back five. If he keeps his feet on the ground and continues to work hard, I have no doubt that he'll play for England.
"He's a terrific player and more importantly a passionate London Irishman. I'm delighted he's extended his contract with us."
Reflecting on the deal, Low said: "I have enjoyed three great years at London Irish and it is great to be here for a further two years."