The Drogheda-born Horgan has scored 18 tries and a drop goal in 51 appearances in the competition.
Former Leinster forward Trevor Brennan, having been replaced by Romain Millo-Chlusky after 48 minutes, cuts a disconsolate figure on the Toulouse bench.
Leinster lock Malcolm O'Kelly competes for a lineout with Jean Bouilhou. O'Kelly, Ireland's most-capped player and now with 54 Heineken Cup appearances behind him, said: "I've been very fortunate in my career, winning Triple Crowns with Ireland. But Saturday was massive for Leinster in terms of getting the monkey of winning in France off our backs.
"There's no better place to win than in Toulouse - the home of the most successful team in Europe. We believed in ourselves and showed the desire we had to win the game. It's great to be involved with Leinster at the moment. We still have a lot to do but beating Toulouse was a fantastic achievement. A performance like this gives us the conviction that we can go on and win the tournament."
Denis Hickie, tackled by Vincent Clerc, stretches for the Toulouse line to score one of the tries of the season.
Hickie grounds the ball for Leinster's third try and his second try in three European games this season. The Ireland winger has now scored 18 tries and a drop goal in 46 appearances in the Heineken Cup.
Leinster number eight Jamie Heaslip tries to snipe through the Toulouse defence. The Kildare man was making only his sixth Heineken Cup appearance on Saturday - the Ireland "A" international scored his one and only European try in the 53-7 thumping of Bourgoin at the RDS in December.
100 not out. Centre Gordon D'Arcy celebrates after his 100th appearance in a Leinster jersey. The province were ending Toulouse's 17-game unbeaten home run in the Heineken Cup.
**All photos by Billy Stickland of Inpho Photography**