He said the plan was to transform the area and make it into the "most liveable town, within the most liveable city".
Once built, the town would offer terraced homes, apartments, stand-alone houses, a primary school, high school, retail developments, green spaces, natural reserves and a retirement village - all interlinked with cycle, walking trails and public transport.
Auckland Council has given the project its stamp of approval, allowing the school's owners, Grafton Downs - a joint venture owned by Wesley College Trust Board and the Methodist Church's PACT 2086 Trust - to rezone its land from Future Urban to Local Centre and Mixed Housing Urban zones.
Council project director of housing Ree Anderson said the development would be the size of a small town.
"The next steps would include supporting Grafton Downs in developing infrastructure to match the needs of a growing town centre."
Real Estate Institute chief executive Colleen Milne said the development presented a great opportunity for buyers.
"The rezoning will open up the Pukekohe area for new infrastructure and should provide new opportunities for those looking to live close to Auckland city."
Pukekohe Business Association manager Kendyl Gibson said the added growth would help increase business capacity and enable residents to work locally. Plans for a high school were particularly welcome.
However, not everyone was so happy.
Past pupil Peter Malcouronne felt "a mixture of sadness and nostalgia" at the news.
Two years ago he'd set up Facebook page SOS Wesley, which had 400-plus members, to rally opposition. Today he was resigned to the development going ahead, but he hoped the profits would stay within the Methodist Church and the college.
"I'd like to see the chapel secured and Wesley transformed and rebuilt somewhere serene and beautiful."
The school's move to a yet-to-be-determined nearby site will be its third. Established in 1844 in Grafton, it moved to Three Kings in 1848, before moving to its current site in 1924. Many of the school's buildings have not borne time well.
Mr Johnston said a new school better suited to current and future learning needs would be built.
Before any land is dug up the finer details need to be finalised, then an application for development consent could be lodged next year.
The college
Wesley College, Paerata, is a state-integrated school with a "special obligation to students of Maori and Pacific Island descent and students whose personal circumstances require special care".
The development plans
• 4500 sections
• 15km of dedicated off-road cycle paths and walkways
• 5ha of neighbourhood reserves
• Two new schools
• A retail precinct
• Retirement village.