Hooker Ford had been a major doubt with a head knock picked up during the Rugby World Cup defeat by South Africa.
Centre Mark Bennett also returns to a side showing seven changes after missing out against the Springboks.
A victory at St James' Park on Saturday would secure Scotland a place in the quarter-finals.
Samoa cannot now qualify and will be without Newcastle Falcons wing Alesana Tuilagi, who has been suspended after foul play during his side's weekend defeat by Japan.
Scotland head coach Vern Cotter said: "Every Test match is a 'must-win' when you represent your country.
"We've put in a huge amount of work to get us to this point and our performances and commitment have put us in a position to qualify for the last eight.
"We'll need to be up to the challenge, enjoy the opportunity and maintain the awareness needed to play to our strengths and impose our game."
Samoa head coach Stephen Betham has also made seven changes and has ensured that, if fly-half Patrick Fa'apale comes off the bench, all but one of his players will have played during these finals.
Cap landmarks for Scotland duo
Maitland returns on the wing to replace Tim Visser, while Bennett takes the place of Richie Vernon at outside centre and fly-half Russell comes in for Duncan Weir.
Alasdair Dickinson and Ross Ford come off the bench to join Willem Nel in the front row, with Gordon Reid and Fraser Brown dropping to the bench,
Ryan Wilson starts in the back row along with Hardie, with Josh Strauss relegated to the bench and Blair Cowan dropping out of the match-day squad.
Richie Gray will earn his 50th cap as he continues in the second row alongside brother Jonny.
Should versatile back Sean Lamont come off the bench, he will become the third Scotland international to earn 100 caps, joining Chris Paterson and women's stalwart Donna Kennedy.
Teams for St James' Park
Scotland: Stuart Hogg (Glasgow Warriors), Sean Maitland (London Irish), Mark Bennett (Glasgow Warriors), Matt Scott (Edinburgh), Tommy Seymour (Glasgow Warriors), Finn Russell (Glasgow Warriors). Greig Laidlaw (Gloucester, captain); Alasdair Dickinson (Edinburgh), Ross Ford (Edinburgh), WP Nel (Edinburgh), R Gray (Castres), J Gray (Glasgow Warriors), Ryan Wilson (Glasgow Warriors), John Hardie (unattached), David Denton (Edinburgh).
Replacements: Fraser Brown (Glasgow Warriors), Gordon Reid (Glasgow Warriors), Jon Welsh (Newcastle Falcons), Tim Swinson (Glasgow Warriors), Josh Strauss (Glasgow Warriors), Henry Pyrgos (Glasgow Warriors), Peter Horne (Glasgow Warriors), Sean Lamont (Glasgow Warriors).
Samoa: Tim Nanai-Williams (Ricoh Black Rams), Paul Perez (Coastal Sharks), George Pisi (Northampton Saints), Rey Lee-Lo (Cardiff Blues), Fa'atoina Autagavaia (Nevers), Tusi Pisi (Suntory Sungoliath), Kahn Fotuali'i (Northampton Saints, captain); Sakaria Taulafo (Stade Francais), Ma'atulimanu Leiataua (Aurillac), Census Johnston (Toulouse), Teofilo Paulo (Benetton Treviso), Kane Thompson (Newcastle Falcons), Maurie Faasavalu (Bath), Jack Lam (Bristol), Alafoti Faosiliva (Bath).
Replacements: Motu Matu'u (Wellington Hurricanes), Viliamu Afatia (Agen), Anthony Perenise (Bristol), Faifili Levave (Wellington Lions), Vavae Tuilagi (Carcassonne), Vavao Afemai (Manu 7s), Patrick Faapale (Manu 7s), Ken Pisi (Northampton Saints).