The ban - which was implemented in 2002 - was intended to prevent terror organisations from gaining access to American silencers.
Silencers - also called suppressors - are devices attached to firearm barrels to mitigate the noise produced when the weapon is fired.
"This is another win for the firearm and suppressor manufacturers by the Trump administration," a spokesperson for the National Shooting Sports Foundation said.
Lifting the ban will allow for as much as $250m in additional sales for the companies Mr Williams formerly represented as legal counsel of the American Suppressor Association.
The decision to lift the ban was justified by the State Department as a market-based attempt to help US manufacturers of the devices. Since foreign entities could not purchase silencers from the US any longer, silencer production rose in other countries.
"US companies should have the same opportunity to compete in the international marketplace as other manufacturers around the world," a spokeswoman for the State Department said.
Making silencers more readily available has been on the Trump agenda since at least 2017. Donald Trump Jr, a trophy hunter and gun enthusiast, backed legislation aimed at making silencers easier to buy for domestic shooters less than a year after his father took office.
The bill - named the Hearing Protection Act - argued that gun owners should be allowed to purchase silencers as a way to protect their ears from the loud sound made from the weapon's discharge.
Noise-reducing headphones and earplugs are common - and suggested - accessories for hobby shooters and hunters.
Ultimately, the bill died in Congress.
Last year, Democrats attempted to push to have the manufacture of silencers completely banned in the US following a mass shooting in which the shooter used one of the devices.