Mair, 52, from Dundee, detailed the attack which took place in December as he was travelling home after having dinner with friends.
Writing in the Sunday Times, Mair described how he was circled by a gang of three youths riding bikes on his way to the bus stop, with one wheeling their front wheel close to his face.
Mair said he attempted to film their behaviour while he waited for his bus to arrive, but was unable to capture their faces as they were wearing hoodies.
The PM presenter wrote that he was struck on the head by one of the three while he was paying for a bus ticket, resulting in a large bruise above his right ear.
Mair said that when two of his fellow passengers offered to help him report the incident to police he felt like he “just wanted to sit down and get home”.
He said he was reluctant to tell authorities what had happened as he felt a sense of guilt about the attack.
He wrote: “I told no one, least of all the police. Not my family or friends. Not work colleagues. I felt shame. I felt I may have been in some way responsible for what happened. Did I goad the little b******s with my video recording?
“As time went on I was increasingly embarrassed I hadn’t reported the crime.
On the bus that night, a woman who came to my aid urged me to report it to try to stop other people being assaulted. That was the most compelling argument for me, but still I resisted.
“For weeks, every time the local paper reported an assault, I believed that I had contributed to it. More shame.”
Mair said he eventually informed the police before he left for a trip to South America.
When he returned to the UK in February officers watched his video of the attackers but had few clues to their identity as their faces were concealed.
They told Mair he should have reported the incident earlier as CCTV footage would have been available for up to a month after it happened.
Mair also revealed that he has his bag stolen during a mugging while he was in South America.
Mair expressed sympathy for comedian Michael McIntrye, who was robbed by a gang of hammer-wielding thieves on mopeds while collecting his children from school.