Kathryn Greiner secures Paddington penthouse through The Agency

The former City of Sydney alderman Kathryn Greiner has settled on a luxury penthouse in Paddington - secured on the quiet through The Agency in a unheralded, much needed break-through sale for the new estate agency.

She has spent $4 million on the whole floor penthouse in the award-winning Paddington Green, former Royal Hospital for Women precinct.

It was sold by LHC Capital co-founder Marcus Hughes, who had bought it three years ago for $2.9 million and secured approved plans to reconfigure the indoor and outdoor living space.

A 213 sqm deep landscaped terrace wraps around the 125 sqm three bedroom apartment.

The off-market sale was secured in May through The Agency's Ben Collier in his first penthouse deal.

The unheralded early August $4 million settlement sits amid the Collier team's $175 million in 2017 sales, of which he's calculated $101 million were off-market.

Collier did not enter the most recent REB Top 100 agents rankings, but his prior personal annual sales tally came in at $278 million.

Greiner served as the City of Sydney Alderman from 1995 to 2004.

She first contested the Sydney City Council election in 1995 as an independent aligned with the Liberal Party.

She outpolled sitting Lord Mayor of Sydney Frank Sartor on the primary vote but lost to him on preferences.

Greiner has served as the chair of the ministerial advisory committee on ageing since 2012.

She is heading an inquiry that will see retirement village operators face new regulations and an inquiry from the NSW Government into the sector after local residents and others campaigned for change.

Greiner is the second daughter of the late merchant banker Sir Bede Callaghan, who was chairman of the Commonwealth Bank and Chancellor of the University of Newcastle.

She may be spending her proceeds of the Illawarra coastal retreat that she shared with her ex-husband, former NSW Premier and Federal Liberal Party president Nick Grenier.

They sold the Otford home last year for $2.9 million to interior designer Thomas Hamel.

In 2014 they sold their Federation-era Centennial Park mansion for $6.25 million to homewares importer Margaret Butler.

The former husband and wife power couple married in 1970 and worked in the USA before returning to Australia. living in the upper North Shore's Wahroonga.

They split in 1995, the same year Kathryn was made Alderman of the City of Sydney. They reconciled shortly after but split again a few years ago.

The Agency is also accepting credit for the $18.75 million sale of the Brett Blundy Cattai estate, Sweven which was marketed by a veteran local agency.

Details on the deal have been supposedly subject to strict confidentiality orders, but The Agency's association didn't go unheralded for long.