Unable to play in Australia's series-opening win last week, Cummins spent a little over an hour bowling with a pink ball to Steve Smith in the SCG nets on Friday morning.
Josh Hazlewood was also in attendance as he attempts to come back from a hamstring injury later in the series, bowling for 45 minutes off a shortened run up.
Cummins is on Friday expected to be named in Australia's squad for the second Test against England at the Gabba, in what would be a massive boost for the hosts.
The 32-year-old has not played in a match since Australia completed a clean sweep of the West Indies in July, where he first noticed soreness in his back.
He has largely taken a wait-and-see approach for the next Thursday's Test, after it was initially identified as a potential return date last month.
But the early signs are good.
Fresh off bowling with a pink ball on Wednesday, Cummins was back in action again on Friday and appeared to be bowling at full speed.
There were no obvious signs of discomfort as he shared the net with fellow Test bowlers Mitchell Starc and Nathan Lyon.
In the next net, Hazlewood and Sean Abbott also showed signs of progressing in their return from hamstring injuries suffered at the SCG a fortnight ago.
Hazlewood ran in at a little over 50 per cent as he bowled at a stump, with Australian officials planning for him to return later in the series.
The quick told 7News there was no timeline for a return but he is "determined" to feature in the series.
Abbott was showing more serious signs of his hamstring injury in the same net as Hazlewood, bowling off a few steps.
The bowling allrounder was part of Australia's initial Ashes squad as a reserve quick, before he and Hazlewood were hurt within hours of each other playing in the Sheffield Shield.
