The 31-year-old has not been capped at senior level but played six times for Scotland's Under-21 side.
Uncapped Bain, 23, was included in Gordon Strachan's initial squad with Hull City's Allan McGregor, 33, rested.
The Scots face Qatar in a friendly on Friday before the Euro 2016 qualifier against the Irish on 13 June.
Celtic's Craig Gordon, 32, and 30-year-old Cardiff City stopper David Marshall are the other keepers in Strachan's squad.
Speaking last week, the national coach explained: "Allan's got a problem that we've known for a year, he's been playing with an injury, and the club and himself want time for that to calm down."
Samson started his career at Killie and had spells with seven other Scottish clubs and Hereford United before returning to Rugby Park in 2013. He has amassed over 300 senior club appearances.
Stoke City's 29-year-old midfielder Charlie Adam and Celtic striker Leigh Griffiths, 24, secured places in Strachan's selection after impressive end-of-season form while Griffiths' club-mate Charlie Mulgrew, 29, also features after recently returning from injury.
Goalkeepers: Craig Gordon (Celtic), David Marshall (Cardiff City), Craig Samson (Kilmarnock).
Defenders: Christophe Berra (Ipswich Town), Craig Forsyth (Derby County), Gordon Greer (Brighton & Hove Albion), Alan Hutton (Aston Villa), Russell Martin (Norwich City), Charlie Mulgrew (Celtic), Mark Reynolds (Aberdeen), Andrew Robertson (Hull City), Steven Whittaker (Norwich City).
Midfielders: Charlie Adam (Stoke City), Ikechi Anya (Watford), Barry Bannan (Crystal Palace), Scott Brown (Celtic), Darren Fletcher (West Bromwich Albion), James Forrest (Celtic), Shaun Maloney (Chicago Fire), James Morrison (West Bromwich Albion), James McArthur (Crystal Palace), Matt Ritchie (Bournemouth).
Forwards: Steven Fletcher (Sunderland), Leigh Griffiths (Celtic), Steven Naismith (Everton), Johnny Russell (Derby County).
Kilmarnock goalkeeper Craig Samson has been called into the Scotland squad to face Qatar and Republic of Ireland after Dundee's Scott Bain withdrew.