At the announcement of the launch of the system for Mojo this morning, Piatek told those gathered that Wellington City Council had allowed them $10,000 in funding from a waste minimisation fund.
She hoped cup-lending would becoming "the thing" in a couple of years, reducing the number of single-use coffee cups being thrown away every day.
Working with Mojo allowed Again Again to "really put some horsepower behind it".
When customers no longer want their keep cup, they can return it for a $3 refund.
Mojo general manager Katy Ellis said it was part of their "whole sustainability story".
Wellington mayor Justin Lester was also at the announcement, and said moving to reusable cups was the next step after eliminating plastic bags from grocery stores.
"Now we've made this change and no unicorns died," he said.
"These are just really basic things to do."
He wanted to see the movement working to eliminate plastic waste "take over the world".
Anyone wanting to find a list of cafes their cups can be taken to for a free swap can head to the Again Again website.