There were few more qualified for the position.
She'd been deputy to Bill Shorten since 2013, held five cabinet positions under the Rudd and Gillard governments, and was among the most recognisable faces in politics.
Yet there she was, "overwhelmed by the confidence" shown to her by her colleagues and party, grateful for their support, but not ready to wield it in the party room.
"Now is not my time," she said.
The decision not to gun for the position, left vacant by Shorten's resignation, stunned and disappointed many. And it was for a reason we've heard from MPs many times before.
For more of Tanya Plibsek's story, including her parents' remarkable journey to Australia, listen to No Filter.
"At this point, I cannot reconcile the important responsibilities I have to my family with the additional responsibilities of the Labor leadership," the statement read.
Speaking to Mamamia's No Filter podcast this week, Plibersek said she simply couldn't "muster the enthusiasm" for the role needed to justify leaving her family even more.
"I was deputy leader the whole time that Bill was the leader, and I had been pretty much on the road six or seven days a week," the 51-year-old said.
"And I thought, 'Well, I know what it's like to be the deputy leader. I know what being opposition leader is like — it's even more time away from home.'"
The Sydney woman's decision was cemented early that Monday morning after the election, when Louis, the youngest of her three children with her public servant husband Michael Coutts-Trotter, came into their bedroom. He was then nine years old then; when she first took the deputy job he was just three.
"He climbed into bed and had a cuddle and was surprised to find me at home at 5am on a Monday morning," she said. "I just thought, 'Wow, what a life for a child to always be missing his mummy.'"