The Royal Marine convicted of murdering a wounded Taliban insurgent will start a life sentence in a civilian prison on Monday after being told he will serve at least 10 years behind bars for betraying and tarnishing the reputation of all British forces.

Jailing Sergeant Alexander Blackman, the first member of the British armed services in recent history to be found guilty of committing murder during an overseas operation, the judge general advocate said the court had to deal with him severely to show the international community that battlefield crimes by UK troops would not be tolerated.

Judge Jeff Blackett said: "In one moment you undermined much of the good work done day in and day out by British forces and potentially increased the risk of revenge attacks against your fellow service personnel."

He accepted it was likely Blackman was suffering from combat stress when he shot the injured prisoner at close range in Helmand in 2011 but added: "It is very important that this court sends out a very strong message that those service personnel who commit crimes of murder, war crimes or crimes against humanity while on operations will be dealt with severely. This is a message of deterrence but it is also to reassure the international community that allegations of serious crime will be dealt with transparently and appropriately."

Blackman, who had completed three tours of Iraq and two of Afghanistan, stood to attention wearing his green beret – beloved emblem of the marines – as the sentence was handed down. He was told he would be "dismissed with disgrace from Her Majesty's service". A court usher was then told: "March out the defendant."

Outside court Blackman's solicitor, Issy Hogg, read out a statement on behalf of the 39-year-old marine and his wife, Claire Warner-Blackman. It said: "Sgt Blackman and his wife are devastated by the life sentence, together with the order that he serve a minimum term of 10 years. He has been dismissed with disgrace from the Royal Marines with whom he has served proudly for 15 years. He is very sorry for any damage caused to the Royal Marines." Hogg said he intended to appeal against the length of his sentence.

Blackman is expected to spend the weekend in military detention at Colchester before being moved to Chelmsford prison, a category B jail in Essex.

Once all legal proceedings involving Blackman and two other marines who were cleared of murder are over, Ministry of Defence officials will consider a wider military investigation into the episode. They may consider whether there was a coverup and whether Blackman was given the support he needed from his superiors during what has been dubbed the "tour from hell".

Privately in military circles there is unease and frustration that Blackman was given what many will consider a harsh sentence, and have huge sympathy for him and his family. Blackman's commanding officer, Lieutenant Colonel Simon Chapman, said he would continue to support the marine. He said: "Fundamentally he is not a bad man. In fact, in almost every respect, he is a normal citizen tainted only by the impact of war."

During mitigation, Blackman's barrister, Anthony Berry QC, said he had been brutalised by the horrors of battle in the "most dangerous square mile in Afghanistan" and had become paranoid that he was always the one being shot at. He and the young marines under his control were in effect working beyond enemy lines fighting insurgents who would have skinned them alive and beheaded them if they had captured them, his counsel said. The corps had suffered heavy losses and by the time of the shooting, Blackman was tired and stressed – and also grieving after the death of his father just before his tour of Helmand began.

The judge advocate general made it clear he and the military board that sentenced Blackman had not been swayed by those who claimed he had committed no crime because the killing was in a combat zone. Blackett said: "Those commentators are very wrong. Hearts and minds will not be won if British service personnel act with brutality and savagery."

During the court martial a video was shown of the moment Blackman shot the dying insurgent, who had been injured in a British helicopter strike. He was heard saying: "There you are, shuffle off this mortal coil, you cunt. It's nothing you wouldn't do to us."

Blackett told him: "You gave him no chance of survival. The tone and calmness of your voice as you commented after you had shot him were matter-of-fact and chilling." He said Blackman had "executed" the prisoner. "You treated that Afghan man with contempt and murdered him in cold blood. By doing so you have betrayed your corps and all the British service personnel who have served in Afghanistan and you have tarnished their reputation."

Blackett said the marine had provided ammunition for Islamist terrorists who would use the case in propagandaists. "That could seriously undermine the reputation of British forces and ultimately the mission in Afghanistan."