However, he has put in a string of impressive performances for Leinster and with Healy left on the replacements bench for Samoa's visit to Dublin, McGrath will pull on the Ireland shirt for the first time.
He is expecting a tough challenge from Samoa, ranked seventh in the IRB list and one spot above Ireland, and especially from his opposite number - Toulouse prop Census Johnston.
"I'm delighted. It is a great honour for me and the family," said McGrath.
"They're a very tough side. The spine of their team is from Top 14 and Premiership, two of the best leagues in the world. For me Census Johnston is going to be a tough operator - I'm looking forward to that challenge."
Ireland head coach Joe Schmidt admitted that loose-head props are not a problem area for him, with a number of contenders pushing Healy for the shirt.
However, the way in which McGrath has challenged the 39-capped prop at in this year's RaboDirect PRO12 and his performance in last year's Amlin Challenge Cup final earned him the nod.
"His form has been really good this year," said Schmidt. "He started in the Amlin Challenge Cup final so there is a bit of confidence in him, having faced up to some pretty good challenges in the past."