Lord Hermer told a human rights lawyer representing Iraqi insurgents that she had "improved lives" whereas British soldiers had not, leaked emails have revealed.
The Attorney General sent the message after evidence emerged at a public inquiry which undermined claims British troops tortured and executed Iraqi civilians.
In the email, obtained by The Telegraph, Lord Hermer said the falsely-accused soldiers could never claim to have "made a real difference to people’s lives" - unlike the lawyer.
Further correspondence revealed the future Attorney General dismissed anger from the military at the cases as "venting".
Lord Hermer has now insisted he has the "greatest respect" for the Armed Forces.
A spokesman added: "These emails simply show the Attorney offering support to a junior lawyer - who was exonerated of any wrongdoing - and who was going through a difficult time.
"It also confirms his view of Phil Shiner, whose actions were reprehensible.
“Over a 30-year legal career, the Attorney General represented many clients, including British military personnel, such as a soldier killed by IRA terrorists and injured servicemen in the Iraq War.
Lord Hermer told human rights lawyers representing Iraqi insurgents they had done more good than British soldiers
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"He always acted with the highest professional standards, and the suggestion he acted for individuals knowing their claims were false is categorically untrue."
The email at the centre of the latest twist, dated to April 2014, shows Lord Hermer voicing his support for a junior solicitor who had not recognised the significance of a key document which emerged during the inquiry.
He wrote to Anna Crowther, a solicitor at Leigh Day: "You should not feel too low about it. There is a much more important big picture: you are making an extraordinary contribution to securing redress for torture victims in Iraq.
"Your hard work, dedication and ability are outstanding and have made a real difference to people's lives - that is not something that Forbes, Neil Garnham or his clients can ever say."
Sir Neil Garnham was the lead counsel for the British troops at the public inquiry, known as the Al-Sweady Inquiry, and his clients included the soldiers falsely accused by the Iraqis.
Lord Hermer, meanwhile, acted as leading counsel for claims of mistreatment by UK troops.
Among cases associated with the claims were accusations of British soldiers murdering Iraqis who were held as prisoners of war at a British Army base.
One of the claims centred around the Battle of Danny Boy in 2004, and resulted in the Al-Sweady Inquiry held 10 years later, however GB News understands Lord Hermer's role in this case was minimal.
The inquiry later concluded the allegations against British forces were “deliberate lies” driven by “ingrained hostility” towards the British Army.
Lord Hermer denies ever acting for Iraqis knowing their claims were false.
General Sir Peter Wall, the commander of British forces in the Iraq War, blasted Lord Hermer's 'apparent disdain for soldiers on the front line'
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Last night, General Sir Peter Wall, a former head of the Army and commander of British forces in Iraq after the 2003 invasion, said: "This latest revelation confirms the mismatch between the Attorney General's role in overseeing the legality of military operations and his apparent disdain for soldiers on the front line and their contribution to the nation.
"This cannot be tenable."
While L/Cpl Brian Wood, who won a Military Cross at the Battle of Danny Boy, said: "It is extraordinary that Lord Hermer thinks lawyers, including himself, acting for Iraqi insurgents do more for society than the soldiers his clients falsely accused of war crimes.
"He is clearly not fit to be Attorney General and must resign."
A Leigh Day spokesman said: "The Solicitors Disciplinary Tribunal ruling completely exonerated the firm and its solicitors of any wrongdoing, including all issues related to the OMS detainee list. This was further confirmed by the High Court in dismissing the SRA's appeal."