Appearing at a parliamentary inquiry in Canberra into the outage, Singtel board director Gail Kelly apologised for the "tragic" failure.
"I sincerely regret the outage that occurred in September of 2025 with its devastating consequences," she said on Thursday.
"We, Singtel, want Optus to thrive. We want Optus to fulfil its obligations to its customers and fulfil its obligations to the Australian people."
The outage lasted almost 14 hours, affected hundreds of calls in four states and territories, and has been linked to two deaths as a result of emergency calls failing to connect.
John Arthur, a Singtel board member and chairman of Optus, said he was "deeply sorry" for the outage and its consequences.
"We have to fix the company and we are," he said.
"I believe we have the right people, right plan and the right oversight to get this company to where it needs to be, and we just have to stay the course.
"I wish it could happen more quickly ... unfortunately, these things, if you are to do them properly, takes time."
Pressed on the issue of foreign ownership, he said Singtel had committed to following all Australian laws.
Mr Arthur said the Singapore-based telecommunications giant had poured $9.3 billion into Optus over the past five years.
Asked if there was truth to rumours the Singtel intended to sell Optus, Ms Kelly repeated the company remained committed to Australia through the telco.
She said Singtel had doubled down to take on the accountabilities of running a fully empowered business.
At the inquiry's previous hearing, Optus boss Stephen Rue admitted a "culture of carelessness" had existed in the lead up to the outage.
He also confirmed it was preparing to cut up to 300 jobs.
Kerry Schott, who completed a scathing independent review into the deadly incident, handed down 21 recommendations and described the failings as "inexcusable".
Representatives from the Australian Communications and Media Authority were grilled by senators over the regulator's response.
The hearing was told the regulator failed to ask further questions from TPG about the death of a customer who couldn't access triple-zero services because of an outage, six days after the fatal September 18 Optus bungle.
Greens senator Sarah Hanson-Young accused the authority of being "asleep at the wheel".
"Their job is to ensure these telecommunications companies are delivering services properly," she said.
"Time and again, they prove that they're just not up to the job."
Officials from the regulator told the hearing it had been "extremely frustrating" to get conflicting information from different parties, or no information at all when it came to outages.
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