The Prime Minister posted a video on Twitter on Friday morning in which he vowed to ban the breed, shortly after West Midlands Ambulance Service confirmed the victim of the Stonnall attack had died.
A 30-year-old man from the Lichfield area was arrested on suspicion of having dogs dangerously out of control and has been further arrested on suspicion of manslaughter.
It comes less than a week after an 11-year-old girl was viciously attacked by an American Bully XL and Staffordshire Bull Terrier crossbreed puppy in Birmingham.
The incident sparked a national outcry and a heated debate over whether the breed should be banned in the UK.
In his video, the Prime Minister said: "The American XL Bully dog is a danger to our communities, particularly our children. I share the nation's horror at the recent videos we've all seen.
"Yesterday we saw another suspected XL Bully dog attack, which has tragically led to a fatality.
"It's clear this is not about a handful of badly trained dogs. It's a pattern of behaviour and it cannot go on.
"While owners already have a responsibility to keep their dogs under control, I want to reassure people that we are urgently working on ways to stop these attacks and protect the public.
"Today I have tasked ministers to bring together police and experts to firstly define the breed of dog behind these attacks, with a view to then outlawing it.
"It is not currently a breed denied in law so this vital first step must happen fast.
"We will then ban the breed under the Dangerous Dogs Act and new laws will be in place by the end of the year.
"These dogs are dangerous. I want to reassure the public that we will take all necessary steps to keep people safe."