Gröning was born in June 1921, in Lower Saxony, the son of a skilled textile worker. His mother died when he was four. His father, a nationalist and strict conservative, joined the Stahlhelm after Germany's defeat in the First World War (during which his father had lost an eye), and his father's anger at how Germany had been treated following the Treaty of Versailles increased as his textile Business went bankrupt in 1929 due to insufficient capital.

Gröning wanted to join an elite army unit and set his sights on joining the Schutzstaffel. Without his father's knowledge, he did so in 1940 at a hotel where the SS was recruiting. Gröning said that his father was disappointed to learn this when he came home after having joined.

One night towards the end of 1942, Gröning and his comrades in their SS barracks on the outskirts of Birkenau were awakened by an alarm. They were told that a number of Jews who were being taken to the gas chambers had escaped and hidden in the woods. They were ordered to take pistols and search the woods. When his group arrived at the extermination area of the camp they saw a farmhouse, in front of which were SS men and the bodies of seven or eight prisoners who had been caught and shot. The SS men told Gröning and his comrades that they could go home but they decided to hang around in the shadows of the woods.

Gröning's application to transfer to a unit on the front-line was successful, and in 1944 he joined an SS unit fighting in the Ardennes. He was wounded and sent to a field hospital before rejoining his unit, which eventually surrendered to the British on 10 June 1945, his birthday.

Gröning and the rest of his SS colleagues were imprisoned in an old Nazi concentration camp. He was later sent to the UK as a forced labourer in 1946 where he had a "very comfortable life". He ate good food and earned money, and travelled through the Midlands and Scotland giving concerts for four months, singing German hymns and traditional English folk songs to appreciative British audiences.

Gröning was released and returned to Germany in 1947 or 1948. Upon being reunited with his wife, he said: "Girl, do both of us a favour: don't ask." He was unable to regain his job at the bank due to having been a member of the SS, so he got a job at a glass factory, working his way up to a management position. He became head of personnel, and was made an honorary judge (a sort of juror) of industrial tribunal cases.

Upon his return to Germany he led a normal life, reluctant to talk about his time in Auschwitz. However, more than 40 years later, he decided to make his activities at Auschwitz public after learning about Holocaust denial. He openly criticised those who denied the events that he had witnessed, and the ideology to which he had subscribed. The recorded accounts he provided to the BBC, however, contributed to the decision and ability to prosecute him. His record as an Activist against Holocaust deniers since 1985 was not taken into consideration. Gröning was notable as a German willing to make public statements about his experience as an SS soldier, which were self-incriminating and which exposed his life to public scrutiny.

Gröning stated that his childhood had been one of "discipline, obedience and authority". Gröning was fascinated by military uniforms, and one of his earliest memories is of looking at photos of his grandfather, who served in an elite regiment of the Duchy of Brunswick, on his horse and playing his trumpet. He told Der Spiegel in 2005, that as a child, he played marbles in the street with Anne Selig, the daughter of a Jewish ironmonger whose store was next to his home. When Nazi storm troopers held up a sign outside the shop saying, "Germans, do not buy from Jews," he said, he was unmoved. He joined the Scharnhorst, the Stahlhelm's youth organisation as a small boy in the 1930s, and later the Hitler Youth when the Nazis came to power in 1933. Influenced by his family's values, he felt that Nazism was advantageous to Germany and believed that the Nazis "were the people who wanted the best for Germany and who did something about it." He participated in the burning of books written by Jews and other authors that the Nazis considered degenerate in the belief that he was helping Germany free itself from an alien culture, and considered that National Socialism was having a positive effect on the economy, pointing to lower unemployment.

In September 2014, it was reported that Gröning had been charged by state prosecutors with having been an accessory to murder for his role at Auschwitz receiving and processing prisoners and their personal belongings. The indictment stated that Gröning economically advanced Nazi Germany and aided the systematic killing of 300,000 of the 425,000 Hungarian Jews who were deported to Auschwitz by 137 railway transports during the summer of 1944. Gröning's prosecution has been reported to have been a part of Germany’s final effort to bring the last Nazi war-crimes suspects to justice. State prosecutors managed to charge the defendant on a legal precedent set in 2011 by the conviction of the former Sobibor extermination camp guard John Demjanjuk by a court in Munich.

On 15 July 2015, he was found guilty of being an accessory to the murder of at least 300,000 Jews. Reacting to the sentence, Auschwitz survivor Eva Mozes Kor said that she was "disappointed" adding: "They are trying to teach a lesson that if you commit such a crime, you will be punished. But I do not think the court has acted properly in sentencing him to four years in jail. It is too late for that kind of sentence ... My preference would have been to sentence him to community Service by speaking out against neo-Nazis. I would like the court to prove to me, a survivor, how four years in jail will benefit anybody." Gröning's defence Lawyer, Hans Holtermann, was quoted as saying that he would review the verdict before deciding whether to appeal. On 28 November 2016, the appeal was declined by the German Federal Court of Justice (BGH). In August 2017 Gröning was considered to be fit for prison. An appeal to the Federal Constitutional Court also failed. The latter court ruled his age was not a valid reason not to send him to jail. On 15 January 2018 Gröning applied for pardon as a last measure to avoid imprisonment. The pardon was rejected.

On 9 March 2018, Gröning died while hospitalized before he was to begin his sentence. He was 96.