Litchfield and Garth were presented their caps by Alex Blackwell and Mel Jones at Trent Bridge on Thursday morning, before Alyssa Healy called right in her first Test as captain.
Australia have opted to go with two front-line spinners, with Jess Jonassen and Alana King picked and Georgia Wareham the bowler to miss out.
The tourists are also without regular captain Meg Lanning, who has been ruled out of the series through illness.
The Irish-born Garth’s debut makes her the first man or woman to represent Australia in a Test match after playing for another nation in any format.
England have also handed out two debuts, with quick Lauren Filer and veteran batter Danni Wyatt to play their first Tests.
The Test match kicks off the multi-format series, with four points on the line in this match and then two points available for each of the three ODIs and three T20s.
The last six women’s Tests have ended in draws, but players are hopeful the use of a Dukes ball and the addition of a fifth day will help reverse that trend.
Australia have held the Ashes since 2015, winning or drawing the past four series.
AUSTRALIA: Phoebe Litchfield, Beth Mooney, Ellyse Perry, Tahlia McGrath, Alyssa Healy (capt), Ashleigh Gardner, Annabel Sutherland, Jess Jonassen, Alana King, Kim Garth, Darcie Brown
ENGLAND: Tammy Beaumont, Emma Lamb, Heather Knight (capt), Nat Sciver-Brunt, Sophia Dunkley, Danielle Wyatt, Amy Jones, Sophie Ecclestone, Kate Cross, Lauren Filer, Lauren Bell.