The 34-year-old, who last played Test rugby in 2017, replaces his Ospreys colleague Dewi Lake.
Lake suffered a knee injury during Ospreys’ Heineken Champions Cup victory over Leicester on Friday.
And the Welsh Rugby Union confirmed that former Harlequins and Worcester forward Baldwin has joined the squad preparing for next week’s Six Nations opener against Ireland in Cardiff.
Captain Ken Owens and Dragons’ Bradley Roberts are the other two hookers in the Wales squad, with Lake and Scarlets’ Ryan Elias among those sidelined through injury.
It is another setback for the highly-rated Lake, who missed Wales’ entire autumn campaign this season because of a shoulder injury.
Baldwin, meanwhile, has won 34 caps, with his latest Wales appearance being against Samoa in Apia.