Urschel, who holds bachelor's and master's degrees and is planning to pursue a doctorate in mathematics at the MIT.
Urschel, who holds bachelor's and master's degrees and is planning to pursue a doctorate in mathematics at the Massachusetts Institute of Technology, did not discuss the reason's for his retirement publicly.
"It wasn't an easy decision, but I believe it was the right one for me," Urschel said in a statement hours after the Ravens announced the news. "There's no big story here, and I'd appreciate the right to privacy."
In January the Canadian-born player told HBO that being knocked unconscious after a helmet-to-helmet hit and suffering a concussion already had an impact on his mind.
"I think it hurt my ability to think well mathematically," Urschel said. "It took me about three weeks before I was football ready. It took me a little bit longer before my high-level visualizations ability came back."
On Thursday, however, Urschel said nothing of health concerns.
"I'm excited to start working on my doctorate in mathematics full time at MIT," he said.
"I'm looking forward to the chance to take courses that are only offered in the fall semester while spending some time with my fiance and preparing myself for the new challenges that will come with fatherhood. We're expecting our first child in December."
Ravens coach John Harbaugh admitted he was surprised by Urschel's move.
"We respect John and respect his decision," Harbaugh said. "We appreciate his efforts over the past three years and wish him all the best in his future endeavors."
In three seasons with the Ravens, Urschel appeared in 40 games with 13 starts, including three last season.
On Tuesday, the Journal of the American Medical Association published a new study in which researchers found striking evidence of chronic traumatic encephalopathy in 110 of the 111 donated brains of deceased players who competed in the National Football League.
CTE causes symptoms including memory loss, vertigo, depression and dementia. Problems can crop up years after a player's career has ended.
The NFL has faced growing scrutiny in recent years linked to the issue of concussions and head trauma, with the league agreeing in 2015 on a $1 billion settlement to resolve thousands of lawsuits by former players suffering from neurological problems.
Though the research -- the largest CTE study published to date -- suggests the disease may be related to prior participation in football, researchers cautioned against extrapolating the results to the general population.
Because the brains studied were for the most part donated by concerned families, they do not necessarily represent all people who have played the rough contact sport.