(Trudeau has since leveraged this to make it clear that when it comes to trade the rest of the world is prepared to move ahead without the protectionist Donald Trump).
A bit of history here.
It is notable that it was Helen Clark's Administration that kicked the TPP ball rolling in the first place.
All being equal, Ardern's Government will bookend the lengthy negotiations when the revised Trans Pacific Partnership (now a new agreement called the Comprehensive and Progressive Trans Pacific Partnership, CPTPP, in a nod to the political coloration of some of the newer leaders) is signed off in Chile in March.
It was Clark who cleared a path with her own caucus for former Labour Trade Minister Phil Goff to go to New York and meet with the then US Trade Representative (USTR) in April 2008 to finalise a move for the United States to join the "P4" (NZ, Chile, Singapore and Brunei).
This was no easy feat.
Clark had after all been offside with the US over the Iraq invasion. Labour was often seen (fairly or otherwise) as "anti-American".
There was internal opposition.
But her Foreign Minister, Winston Peters, had already led a successful charm offensive with then Republican Secretary of State Condi Rice to restore relations.
Goff and USTR Susan Schwab also forged common ground before announcing an intention for the US to join an expanded P4 as the first step towards an ambitious Asia-Pacific deal that would ultimately bring 12 nations into its orbit before Trump pulled America out.
This thesis is not fanciful.
Let's just underline here that New Zealand's role in TPP has always been much larger than mere negotiating clout.
Other nations acknowledged the street cred that successive New Zealand Governments and officials had brought to the table in fashioning the ambitious goal.
This resulted in this country being installed as the "depository" for the TPP.
The onus has since been on New Zealand to keep negotiations moving.
That's why former National Party Trade Minister Todd McClay criss-crossed the Pacific for months in 2017 to work with Japan to reinvigorate TPP after Donald Trump pulled the pin on US participation.
The original TPP would have covered 40 per cent of the global economy.
Having greater access to the US would have assisted NZ exporters. But it is significant that Japan's protections against NZ agricultural exports will diminish once the new deal goes into effect.
Other nations such as South Korea and Indonesia have expressed interest in joining.
The way is also clear for the United States "to dock" at a future date.
Ardern acknowledged yesterday that the deal wasn't perfect.
But at time of rising protectionist sentiment led by the United States it is important that moves towards freer trade are not sent into reverse.
There will be opposition from some protesters who focus on negatives to the exclusion of real gains.
But assuming the CPTPP is finally signed in March we should salute two Prime Ministers. Both Labour. Both female — and both utterly pragmatic when it comes to forging a deal — to the point where they (like all the pros in complex negotiations where no one ever gets all they want) have been principled enough to stake some bottom lines but also flexible enough to know when to swallow the odd dead rat to get it nailed.