In the weeks leading up to the Rising, he acted as bodyguard for
Thomas Clarke. Before the Rising, because he lived out of the city he stayed with the
Cooney family in the city centre. During Easter Week, he fought at Watkin's Brewery, Jameson's Distillery and Marrowbone Lane.
Thomas MacDonagh at 3.15 p.m. Sunday, 30 April surrendered to
Brigadier-General Lowe. MacDonagh then went around the garrisons under his command to arrange for their surrender. Colbert surrendered with the Marrowbone Lane Garrison along with the South Dublin Union Garrison, which had been led by
Éamonn Ceannt. It has been claimed that when the order to surrender was issued, he assumed the command of his unit to save the life of his superior officer, who was a married man. However, this seems to have been a matter of luck - the well known Colbert was picked out immediately by Dublin detectives who had often seen him drilling Fianna Éireann and speaking at anti-recruiting meetings. They were marched to Richmond Barracks, where Colbert would later be court-martialled. Transferred to Kilmainham Gaol, he was told on Sunday 7 May that he was to be shot the following morning. He wrote no fewer than ten letters during his time in prison. During this time in detention, he did not allow any visits from his family; writing to his sister, he said a visit "would grieve us both too much". ==Execution==