Mr Machin said the website would return to operations gradually, with 85% of the range back "quite quickly".
M&S is now three years into a turnaround strategy, started when Mr Machin joined as chief executive in 2022.
It involves updating in-store ranges and the chain's property portfolio, with digital technology and back-office systems also set to be overhauled.
The strategy had put M&S in it "best financial health for nearly 30 years" Mr Machin said, delivering results for the financial year ending in March just before the hack disrupted services at the end of April.
M&S reported a 22% rise in profit before tax and other costs to £875m, while sales rose 6.1% to £13.9bn, with growing food sales taking the lead.
Mr Machin said the cyber-attack had highlighted "new and innovative ways of working".
"If anything, the incident allows us to accelerate the pace of change as we draw a line and move on," Mr Machin added.
But it will also weigh on M&S's profits for the current year, with food sales hit by reduced availability, the company said.
In fashion home and beauty, online sales were lost due to the pause in online ordering.
Meanwhile, additional waste and logistic costs, including needing to use manual processes, have affected profit.
Mr Machin admitted that the £300m hit to profits "does sound like a big number, but it is a one-off number".
Around half would be offset by reducing costs and from the company's cyber-insurance policy, he said.
While insurance is expected to cover perhaps a third of the bill, there could be further charges to consider including fines for the data loss, litigation, and future-proofing the business from new attacks.
Lucy Rumbold, equity research analyst at Quilter Cheviot, said it would be "a long slog" for M&S to get back to where it was.
"But given the strong performance of late and provided the attack can be wholly eliminated, the business should get there," she said.