The 21-year-old Cummins returns to the national squad for the first time since June 2012, and Starc is on the comeback from a groin strain.
Johnson, unveiled last week as the 2014 international cricketer of the year, played the first two ODIs in Perth but will take a break ahead of the test series against India starting December 4.
South Africa won on Sunday to level the ODI series, which now heads to Canberra, Melbourne and Sydney.
"We have decided to add two extra pace options ... That also gives us the opportunity to ensure Mitchell Johnson is fresh and well prepared ahead of the first test against India," Marsh said Monday.
More From This Section
Cummins has played one test, five ODIs and 14 T20 internationals for Australia and is considered a potential long-term leader of the attack. His international career starting promisingly when he took seven wickets on test debut in a series-leveling win in South Africa in 2011 at the age of 18.
But the tall, right-arm fast bowler has been sidelined for long periods since then with lower back problems. Xavier Doherty was drafted in to the squad as the spin specialist, preferred to regular test offspinner Nathan Lyon.
Squad: George Bailey (captain), Nathan Coulter-Nile, Pat Cummins, Xavier Doherty, James Faulkner, Aaron Finch, Josh Hazlewood, Mitchell Marsh, Glenn Maxwell, Kane Richardson, Steve Smith, Mitchell Starc, Matthew Wade, David Warner, Shane Watson.