Bovil Peter and Patrick Beckford were both support staff workers at the jail, and were believed to be aged in their 60s.
POA national chairman Mark Fairhurst said: “My thoughts and prayers are with everybody involved with these tragic deaths – two at the same prison is very concerning.”
Mr Fairhurst said he did not know if either of the men had any underlying health conditions.
He described Mr Peter as “an experienced member of staff” who was working at operational support grade at the prison, and “he died earlier this week due to Covid-19 symptoms”.
Mr Fairhurst added of Mr Peter’s death: “I just want to highlight the fact that this (Covid-19) puts us all at risk.
“We are on the front line doing a commendable job on behalf of society and he will be sadly missed by all his colleagues. We wish the best for his family and friends.”
It is believed staff at the prison paid tribute with a minute’s silence after hearing their colleagues had died within days of each other earlier this week.
A Prison Service spokesman said: “Two staff members at HMP Pentonville have sadly passed away, and our deepest sympathies are with their loved ones and colleagues at this difficult time.”
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