Hooker Matthew Rees also returns to the side with Huw Bennett, who started the recent defeat to France, moving to the replacements bench.
Lock Luke Charteris keeps his spot after coming on for the injured Deiniol Jones early in the first half of the French game.
Elsewhere, Wales head coach Warren Gatland has said 'same again' to his back-line for the third game in-a-row and made two changes on the bench with the inclusion of scrum half Dwayne Peel and lock Ian Gough.
Gatland said: "We have taken the decision not to include any players who are unable to take a full part in training in the build-up to the Ireland game.
"This Ireland side will be meticulous in its planning and for this game in particular we need to get our preparation exactly right and once we had reached that conclusion, a couple of selection decisions were really made for us.
"Ryan has been managing his calf, but it has hampered his involvement in training and he needs to get it right for his own sake as well as for his region, who have some big matches of their own coming up, and for the sake of the national cause as we countdown to the World Cup.
"Mike (Phillips) is carrying a knock which he picked up on Ospreys duty at the weekend and so was not in contention.
"But this is an opportunity for Martyn (Williams), who is one of our key leaders, to captain Wales again and rise to that challenge after doing a good job against Scotland last year when Ryan was again forced to withdraw."
Flanker Williams captains his country for the seventh time and also wins his 95th cap, making him Wales' most-capped forward and now just five appearances behind the country's most capped player Gareth Thomas.
WALES Team & Replacements (v Ireland, 2010 RBS 6 Nations Championship, Croke Park, Saturday, March 13, kick-off 2.30pm):
15 - Lee Byrne (Ospreys)
14 - Leigh Halfpenny (Cardiff Blues)
13 - James Hook (Ospreys)
11 - Shane Williams (Ospreys)
10 - Stephen Jones (Scarlets)
9 - Richie Rees (Cardiff Blues)
1 - Paul James (Ospreys)
2 - Matthew Rees (Scarlets)
3 - Adam Jones (Ospreys)
4 - Bradley Davies (Cardiff Blues)
5 - Luke Charteris (Newport Gwent Dragons)
6 - Jonathan Thomas (Ospreys)
7 - Martyn Williams (Cardiff Blues) (capt)
8 - Gareth Delve (Gloucester)
16 - Huw Bennett (Ospreys)
17 - Rhys Gill (Saracens)
18 - Ian Gough (Ospreys)
19 - Sam Warburton (Cardiff Blues)
20 - Dwayne Peel (Sale Sharks)
21 - Andrew Bishop (Ospreys)
22 - Tom Shanklin (Cardiff Blues)