People across the UK paused at noon to reflect on last Friday's atrocity and remember the 38 people who were killed in the beach front massacre.
The tribute happened as the funeral of two of the three Irish victims of the atrocity's funeral was held in Athlone.
Father Liam Devine said the deaths of Larry and Martina Hayes, who had been married for 32 years, were "unprecedented. Unreal. It is almost impossible to come to terms with it."
In Britain, the Queen and the Duke of Edinburgh observed the silence as they visited the University of Strathclyde's Technology and Innovation Centre, while Prime Minister David Cameron marked the moment in his Oxfordshire constituency.
Just before the silence, an inquest was opened into the death of engineer Stephen Mellor, from Bodmin, Cornwall, who was killed as he shielded his wife Cheryl during the beach massacre a week ago.
West London Coroner's Court heard that Mr Mellor was killed by gunshot wounds to the chest and abdomen.
The hearing was told that 275 witness accounts had been taken by police, while more than 1,200 potential witnesses had returned to the UK.
As pedestrians and tourists alike bowed their head in London's Parliament Square during the silence, flags above Whitehall fluttered at half mast, a poignant symbol mirrored at public buildings throughout the country, including at Buckingham Palace.
According to Tunisian officials, gunman Seifeddine Rezgui trained at a Libyan jihadist camp at the same time as the two gunmen who attacked the Bardo museum in Tunis in March, killing 22 people.
It is believed Rezgui - who was shot dead by police - had accomplices who helped him to carry out the atrocity and the Tunisian government said it had made a number of arrests.
Eight people - seven men and one woman - were in custody, suspected of having direct links to the massacre, but four others had been released, government minister Kamel Jendoubi said.
