Mr Akbari had been accused of spying, an allegation which he denied, and the Iranian Students’ News Agency confirmed his execution on Saturday.
British Prime Minister Rishi Sunak condemed the execution, describing it as “callous and cowardly”.
“I am appalled by the execution of British-Iranian citizen Alireza Akbari in Iran,” he wrote on Twitter on Saturday.
“This was a callous and cowardly act, carried out by a barbaric regime with no respect for the human rights of their own people. My thoughts are with Alireza’s friends and family.”
Mr Akbari, who previously worked in Iranian defence, was first arrested in 2019 and accused of espionage for MI6 related to past nuclear talks between Iran and western nations.
On Saturday, Iranian state media said he was “was sentenced to death on charges of corruption in the land and widespread action against the country’s internal and external security through espionage for the intelligence apparatus of the British government.”
British foreign secretary, James Cleverly, calIed for the immediate release Mr Akbari this week.
“This is a politically motivated act by a barbaric regime that has total disregard for human life,” he wrote on Twitter on Wednesday.
On Saturday, the foreign secretary said: “The execution of British-Iranian Alireza Akbari is a barbaric act that deserves condemnation in the strongest possible terms.
“Through this politically motivated act, the Iranian regime has once again shown its callous disregard for human life.
“This will not stand unchallenged and we will be summoning the Iranian Charge d’Affaires to make clear our disgust at Iran’s actions. Our thoughts are with Mr Akbari’s family,” he concluded.
Earlier this week, the family of Mr Akbari said they had been asked to go to his prison for a “final visit” and that he had been moved to solitary confinement.
There was no immediate reaction from them following his execution.
Iranian state media previously aired a highly edited video of Mr Akbari discussing the allegations resembling others that activists have described as coerced confessions.
During the video, he was asked about the assassination of Iran’s top nuclear scientist, Mohsen Fakhrizadeh, who was shot dead in 2020.
“They wanted to know about high-ranking officials depending on the major developments ... for example he (the British agent) asked me whether Fakhrizadeh could be involved in such and such projects and I said why not,” Mr Akbari said in the clip.
Iran has been rocked in recent months by anti-government protests following the death of 22-year-old Mahsa Amini, who was arrested by morality police in Tehran for allegedly breaking the country's strict dress code.
She collapsed at a detention centre and died three days later in hospital and in recent weeks, Iranian authorities have executed a number of the alleged protesters, such as a karate champion and a volunteer children’s coach.