Marine Sam Alexander, 28, from Hammersmith, west London, and Lieutenant Ollie Augustin, 23, from Kent, were killed on Friday when they were caught in a blast from an IED (improvised explosive device).
The men were both in 42 Commando Royal Marines.
The men were on patrol in the Loy Mandeh area of the Nad-e Ali District of Helmand Province when they were killed, an MoD spokesman said.
Marine Alexander was awarded the Military Cross for gallantry during a previous tour of Afghanistan.
Colleagues said he embodied the attributes of a Royal Marines Commando and was "courageous, selfless, resolute".
As well as his wife Claire, he leaves his son Leo, mother Serena and father Stuart.
Lt Augustin, who was leading the patrol on Friday, leaves his father Sean, his mother Jane and his sister Sarah.
Marine Alexander joined the Royal Marines in 2006.
In 2009, during deployment in Afghanistan, he saved the life of a wounded colleague by charging at the Taliban with his pistol to provide cover.
He was awarded a military accolade for his bravery by the Queen at Windsor Castle in December 2009.
The citation for his Military Cross said he carried out his brave actions "despite being completely exposed to heavy and accurate enemy fire".
He trained as a heavy weapons specialist and was appointed to Juliet Company before returning to Afghanistan.
His wife Claire, the mother of his one-year-old son, said: "Sam was so special. He was the gentlest of men but tough when he needed to be. He risked his safety for his friends but never batted an eyelid.
"Sam was a loving husband and a wonderful father. He was our rock and my best friend. He has been taken from me all too soon. We both love him and will miss him very much."
His father Stuart added: "Sam's professionalism was widely acknowledged, the award of a Military Cross is testament to his courage and care for those around him. But it is as a father and husband that he showed the same deep-rooted wish always to help and care for others.
"People say I must be very proud, but the respect in which I held him was more important than pride. He was a great guy with a great smile and a zest for life. I loved him very much."
Marine Alexander's mother Serena added that he would "never be forgotten".
The Marine's commanding officer, Lieutenant Colonel Ewen Murchison, said he was a "truly remarkable" man.
He said: "Decorated during his last tour of Afghanistan for gallantry, he embodied all the finest attributes of a Royal Marines Commando: he was courageous, selfless, resolute, loyal and cheerful in the face of adversity.
"He was a larger than life character and leaves a gap that cannot be filled. One of the more senior Marines in Juliet Company, he inspired those around him to reach the highest possible standards and in doing so was an exemplary role model for those younger and less experienced than himself."
Marine Brett Newman said Marine Alexander would "always have a laugh with the lads".
He said: "He thought the world of his wife and son, Leo, who Sam thought would be the next Lewis Hamilton despite the fact he was still in nappies. He was a very good mentor to the new lads."
Captain Rob Garside said Marine Alexander was the one "that everyone would want to be by his side in a firefight".
Marine Jason Badham added: "Marine Alexander MC, a true hero, always full of morale, a real inspiration to us all and he will be greatly missed."
Defence Secretary Dr Liam Fox said: "As a holder of the Military Cross for gallantry, Marine Alexander demonstrated some of the finest attributes of a Royal Marine Commando and was clearly held in high regard by his colleagues.
"The ultimate sacrifice that he has made for the safety of others will not be forgotten. My thoughts are with his friends and family at this difficult time."
Lt Augustin attended Dartford Grammar School in Kent until he was 18 when he left the UK to spend a year travelling.
When he returned from his travels he was employed as a fitter and plasterer while applying to become a Royal Marine.
He began his training in 2009 and was passed fit for duty in December last year.
An MoD spokesman said his first appointment was in Command of Fire Support Group, Juliet Company, 42 Commando Royal Marines.
His colleagues said he was a passionate and selfless leader.
His parents, Jane and Sean, said they would "love and miss" their son forever.
They said: "Ollie was a much loved and cherished son. He was a beautiful boy who we were very proud of. He had many friends that he loved and who loved him in return.
"His warmth and humour lit a room and infected all around him. He dealt with people in a thoughtful and compassionate way. His independence and sense of adventure meant that he embraced life and his chosen path."
His sister Sarah added: "Ollie, you were a one in a million. You were brave, you were funny and I couldn't have wished for a better brother.
"You were so very special and made a lasting impression on anybody lucky enough to meet you."
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