The tight-head has been back to his dominant best in the Guinness Premiership in recent games and has now moved ahead of Adam Jones in the thinking of Wales head coach Gareth Jenkins.
And Horsman, who will start in the front row with Rhys Thomas and Gethin Jenkins, admits he has his Worcester team-mates to thank for his start at the Millennium Stadium.
"With the way the Worcester pack is going I was confident I could push for a starting place. They have really helped me," said Horsman, who celebrated his 30th birthday on Friday.
"I am here because of what I have achieved with my mates at Worcester. We are a close bunch of guys that has not fragmented despite what we have been through recently.
"We have started to play better in the last few weeks and that has definitely helped me earn my place for Wales."
Horsman admits he can hardly wait to pull back on the red jersey of Wales and try to upset the Six Nations favourites in Ireland.
But away from the international arena he insists his club future remains at Worcester and working alongside Director of Rugby John Brain.
"Everyone knows what I think about John Brain as a coach and a man - I have got tremendous respect for him.
"I am under contract and I love it at Worcester, everyone is well aware of the relationship I have with John Brain and Cecil Duckworth. I am under contract and if I'm asked to honour that, and the club want me, I will do so happily."