The 22-year-old Carr made his senior debut for Leinster against Glasgow Warriors in October but his chances have been limited at Leinster and it has been in the AIB League where he has been starring in recent seasons.
The Newbridge youngster scored 325 points (23 tries) for Blackrock College over the past three AIB League seasons and his semi-final heroics - ironically against Keatley's Clontarf side - helped them reach their first ever AIB Cup final last month.
Carr, who has bags of paces and an accurate right boot, gained 10 Ireland Under-21 caps in recent years and this season he took his Leinster 'A' caps tally to 15.
Keatley's greatest achievement on the pitch to date was of course being the out-half in the Grand Slam-winning Ireland Under-20 team of 2007.
The highly-rated 21-year-old continued his development this season by lining out for Clontarf in AIB League Division One, scoring 79 points in the process.
The former Belvedere College pupil has been capped by Ireland from Under-18 level up to the Under-20s and he also made his debut for the Ireland 'A' side against Scotland in the Churchill Cup last June.
The possessor of a strong right boot and good play-making ability, Keatley converted his own try in the Leinster 'A' team's 22-7 defeat to their Connacht counterparts in February.
Connacht CEO Gerry Kelly sees Carr and Keatley as having great potential and reckons they are sure to benefit Connacht in the coming season.
"We're delighted to announce that we've signed two exciting prospects for the coming season," Kelly said.
"Fionn and Ian have both shown great ability at age group levels for Ireland and it is our hope we will develop them into future Irish internationals."