Chief commercial officer Paul Harker will give evidence to the Federal Court in the case brought by the Australian Competition and Consumer Commission, which claims Woolies temporarily hiked prices before reducing them to disguise increases.
The ACCC launched the joint action against Woolworths and Coles in 2024 in response to their respective "Prices Dropped" and "Down Down" marketing campaigns.
Coles offered its defence in February in a 10-session hearing, but the court's final judgment will be withheld until each supermarket giant's case is heard.
Mr Harker is no stranger to the witness box, having appeared before Senate committees and state inquiries into living costs, pricing and supply chain issues.
He gave evidence in the ACCC's year-long inquiry in 2024 relating to accusations of price gouging, of which the regulator ultimately found no evidence.
In the first session of a scheduled eight-day hearing on Monday, ACCC lawyers  accused Woolworths of employing "subtle magic" in its pricing campaign to disguise price hikes with outsized, short-term increases before reducing them to above the original shelf price.
The commission said the supermarkets offered certain products at a regular price for at least 180 days, hiked their price by at least 15 per cent for a "relatively short period of time", before reducing them to above the original shelf price alongside "Prices Dropped" or "Down Down" tags.
Justice Michael O'Bryan said on Monday the case would hinge on the duration of the temporary price hike.
"If the price establishment period was three months, we wouldn't be here," he told the court.
"If it was always one week, the case might not be fought.
"We're somewhere in the middle and that's what makes this case rather difficult."
Woolworths' legal team called the watchdog's claims misguided and said the price growth was rooted in supplier negotiations and came against a backdrop of post-COVID pandemic inflation.
It noted price growth had been relatively uniform across Australia's three biggest supermarket chains, which also includes Coles and Aldi.
The ACCC alleges the conduct involved 266 products at Woolies and 245 goods at Coles at different times between late 2021 and mid-2023, impacting tens of millions of sales and deriving significant revenue for the grocery giants.
The basket was whittled down to 12 agreed items to be scrutinised in court, including a Tim Tams Family pack, Carman's classic fruit and nut muesli bars and Sakata rice crackers.
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