Shortly afterwards, Sophie Pascoe took out the women's 200m individual medley SM10.
Boyle's gold medal adds to the silver she won yesterday in the 800m freestyle.
It is the first time New Zealand has won a Commonwealth gold in the 400m freestyle event.
With eight blazing lengths of the pool in Glasgow, Boyle finally ended New Zealand's 20-year wait for a gold medal in women's able-bodied swimming.
Not since the Auckland Games in 1990, when Anna Simcic was crowned in glory, had New Zealand reached these heights.
This was a majestic swim from the 26-year-old, breaking the Commonwealth Games record with a time of 4 minutes and 04.47 seconds. Wales' Jazz Carlin took silver, while Australia's Bronte Barrett claimed the bronze.
The race got off to a fast start. Boyle, content to keep in touch of the early leaders, didn't push too soon.
But she took the lead at the halfway point and didn't let it go.
Pascoe put in a dominant performance in her event this morning, winning by a margin of four seconds from her closest rival, Australia's Katherine Downie. Canada's Aurelie Rivard claimed the bronze medal.
It is Pascoe's second gold of the Games, following on from her victory in the 100m breastroke SB9.
