Murphy said during a news conference in Trenton that "admittedly" it would be hard to enforce, but pointed to the rate of transmission of the virus creeping higher. The rate, which represents how many people one infected person spreads the virus to, has climbed from about 0.7 to 1.1 on Wednesday, the governor reported.
"If you're in your bubble with your family or sitting by yourself or doing something on your own, that's not our focus," he said.
He added that the focus is where you can't socially distance around strangers, such as in a slow-moving line.
"We feel pretty strongly this is the right step to take, one that I hoped we wouldn't have to take," Murphy added.
The order exempts people eating outdoors, those with some medical conditions and infants under 2 years old.
The order also exempts situations when wearing a face covering would inhibit an individual's health, such as engaging in high intensity aerobic or anaerobic activities, when in the water, and in other situations where the presence of a mask would pose a risk to the individual's safety.
Masks are already required indoors in New Jersey and are currently encouraged to be worn outside.
The new order comes as New Jersey's COVID-19 trends had been headed largely in the right direction, while many other states, particularly in the south and west, are seeing spikes.
Meanwhile, Murphy said there are several outbreaks across the state that have been directly tied to COVID-19 hotspots across the country. There is a 14-day quarantine for those who travel from those hotspots.
As of Tuesday, there are 19 states on New Jersey's quarantine list: Alabama; Arkansas; Arizona; California; Delaware, Florida; Georgia; Iowa; Idaho; Kansas; Louisiana; Oklahoma, Mississippi; North Carolina; Nevada; South Carolina; Tennessee; Texas; and Utah.
Individuals who are traveling to New York, New Jersey or Connecticut from impacted states for business are exempt.
New Jersey has about 174,000 positive cases, with about 13,500 confirmed fatalities. There are an additional 1,947 deaths likely stemming from COVID-19, Murphy reported Wednesday.
For most people, the virus causes mild or moderate symptoms. Older adults and people with existing health problems are at higher risk of more severe illness or death.