The 23-year-old had surgery last summer after a heavy collision in a Pro12 game in March 2015 forced two discs in his back to protrude onto his spinal cord.
He won three international caps, scoring two tries, but has not played for Scarlets since December 2015.
"I am utterly devastated and it is a very, very bitter pill to have to swallow," said Robinson.
"I never thought I would be in this position at the age of 23 - having to call an end on my professional rugby career at such an early age.
"I have worked so hard over the last 10 months to return to full fitness and regain the functionality I had before the injury.
"It is with great regret that I have been unable to do this."
Robinson joined Scarlets in 2014 from Cardiff Blues and went on to make 30 appearances for the region.
A Wales Under-20 international and former member of Wales Sevens squad, Robinson was called into the senior squad for the training camp in Poland in January 2012 before that year's Six Nations Championship.
Robinson scored his first international try on his debut against the Barbarians in June 2012 at the Millennium Stadium.
"Whilst I am devastated I count myself very lucky and enormously privileged," he said.
"I have had a fantastic six years as a professional rugby player with both Cardiff Blues and Scarlets.
"I have travelled all over the world at every age grade, Wales Sevens and the Welsh squad."
Jon Daniels, Scarlets' general manager of rugby, said: "It is with great sadness that we as a region have to confirm Harry's retirement from rugby.
"He's a talented young player who had a bright rugby future ahead of him.
"It has been a difficult time for Harry as he has worked exceptionally hard to make a full recovery.
"I am sure the qualities that got him to the top of the rugby tree in Wales will stand him in good stead in his future career."
Scarlets play Newport Gwent Dragons on Saturday in Welsh rugby's Pro12 Judgement Day IV at Principality Stadium.
Wales and Scarlets wing Harry Robinson has retired from rugby with immediate effect following a serious neck injury.