The defiant visiting fans broke the minute's silence held before the game to mark Friday's tragic events in Paris to sing the French national anthem, and their side responded by taking an early lead through a Francois Bouvier penalty.
However, Irish were heavy favourites on their home ground against the competition's lowest-ranked side and it took them just 10 minutes to find a way through for the first try as Johnny Williams crashed over after good work from Darren Allinson to mark his debut for the club in style.
The visitors responded well initially, pinning the home side back and forcing some fine defensive work to prevent them breaking through, but they found themselves with a mountain to climb with 23 minutes gone when hooker Gerard Ellis burst through a gap to drive home from 20 metres and extend the lead.
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Joe Trayfoot added a debut try of his own after half an hour as the Exiles began to move through the gears, and Ellis went over for his second to secure the bonus point before half time as the hosts went into the break in control at 24-3.
Just two minutes after the restart Alex Lewington latched on to Chris Noakes's chip to improve the scoreline further, and when Rob McCusker strolled over unchallenged and Sean Maitland scored his first for the club, it seemed to be a matter of how many Irish would score.
However, Agen enjoyed their best spell of the game and finally found a reward for their perseverance when Felicien Vergnon squeezed over for a consolation.
There was still time for Lewington to add Irish's eighth and final try with his second of the afternoon as the Aviva Premiership strugglers recorded an emphatic start to their European campaign.