He attributed the move to “segment shifts" across Europe, highlighting the growing trend for SUVs in place of models such as the Astra, which is built at Ellesmere Port.
The news in October that the plant near Liverpool would scrap 400 roles came three months after French car maker PSA Group, which also owns Citroën, DS and Peugeot, completed its acquisition of Vauxhall and its European counterpart Opel.
At the time, PSA said manufacturing costs at Ellesmere Port were higher than other "benchmark plants" in the group.
The facility will move staff from two production shifts to one in early 2018.
Since then, PSA and Vauxhall/Opel has announced a turnaround plan that includes launching all cars on PSA platforms and setting the goal of keeping all current plants – including Ellesmere Port and Luton in the UK – open, although potentially on altered terms.
Harvey said today: “I'm very excited in terms of what's going on. There's a lot of transition, a lot of change. But if you look at some of the fundamentals now, we're moving very swiftly.
“One thing that isn't necessarily a positive, but happened on a voluntary basis, is that we took some cost out of the plant at Ellesmere Port and some people put their hand up to help us get to where we need to.
"That's nothing to do with output or performance, but segment shifts in the market throughout Europe. When you've got one product on a line, if you get shifts in market you have to align your resources.”
Harvey continued: “I've been a Vauxhall employee for 28 years and it feels a bit different to have a new owner. But we have to get on the front foot and we have to get the business turned around, and we have to get ourselves in a competitive position. Vauxhall has a great heritage.”
He also acknowledged that next year will be a challenge for the car industry in terms of sales, with uncertainty this year likely continue.
Talking about 2018, Harvey said: “We think Q1 may be down on this year, and Q2-4 will be flat.”