Cahill hurt his knee in Sunday's game against West Ham and will not play against San Marino but will be reassessed ahead of Tuesday's game against Montenegro.
Taylor has been called up following some impressive recent performances in the Barclays Premier League.
"It's a dream come true," he told nufc.co.uk.
"I am so happy to have received a call-up to the full squad. It is every player's ambition to represent their country and it is the greatest honour in professional football.
"If I am lucky enough to be given that chance over the next seven days it will be one of the proudest moments of my playing career."
Newcastle boss Alan Pardew added: "This is a fully deserved call-up for Steven.
"He missed part of the season but since his return he has been outstanding.
"He has a great chance, on this form, of going to the World Cup."