Both have been rewarded for strong finishes to the Ryobi Cup season and will play important roles in Michael Clarke's side as Australia bid for their third straight Champions Trophy title in England starting in June.
It is the first time the 25-year-old Coulter-Nile has earned a call-up to the 50-over squad while the injury-plagued Marsh, 21, played one ODI during Australia's 2011 tour of South Africa.
The last batting position was decided between two other Western Australians, with Adam Voges edging out Mitch's brother Shaun Marsh on the back of his century in the one-day series final against West Indies earlier this year.
Ben Cutting, Steve Smith, Aaron Finch and Moises Henriques were the players dropped since the last one-day series. Twenty20 captain George Bailey has been retained and will act as Clarke's deputy, with reincarnated veteran Brad Haddin not chosen and Matthew Wade the only wicketkeeper named.
James Pattinson and Ryan Harris, considered the spearheads of the Test pace attack, have not been selected and will instead play red-ball cricket for Australia A to prepare them for the Ashes.
"Coulter-Nile is an emerging cricketer as a fast-medium bowler and explosive lower-order batsman," chief selector John Inverarity said.
"He is also one of the finest fieldsmen in Australian cricket and the energy he brings to his game is impressive. While Nathan has played a T20 International for Australia, we are looking forward to seeing him take his very good domestic limited overs form onto the world stage."
Australia have been drawn to play England, New Zealand and Sri Lanka in the group stages, starting against the hosts on June 8 at Edgbaston.
Australia Champions Trophy 15-man squad: Michael Clarke (c), George Bailey (vc), Nathan Coulter-Nile, Xavier Doherty, James Faulkner, Phillip Hughes, Mitchell Johnson, Clint McKay, Mitchell Marsh, Glenn Maxwell, Mitchell Starc, Adam Voges, Matthew Wade, David Warner, Shane Watson.
- Sports & Recreation
- Shaun Marsh
- Adam Voges