Bath player Ford, 23, missed six out of seven kicks at goal during the 27-13 victory over Wales 11 days ago.
That - combined with 24-year-old Farrell's form for title-winning Saracens - has convinced coach Eddie Jones to make the change.
Luther Burrell is likely to take the inside-centre role vacated by Farrell.
Harlequins winger Marland Yarde is in line to start instead of Exeter's Jack Nowell, with England to confirm their team at 10:00 BST on Thursday.
England have never won a series in Australia, but are determined to overturn the 33-13 "hiding" they were given by the Wallabies at the 2015 World Cup.
"We came out of that game thinking we had thought too much of ourselves," said loose-head prop Mako Vunipola of England's heaviest defeat on home soil.
"The biggest lesson we took was that on any day anything can happen. We go into this weekend knowing that too.
"There is no thought of revenge or righting wrongs of the World Cup and, although it's hard to forget, it has got to go to the back of our minds."
George Ford is expected to make way for Owen Farrell at fly-half for England's opening Test against Australia in Brisbane on Saturday.