Constable Frank O'Reilly, 30, lost an eye and suffered other injuries in the incident in September. The attack took place during protests, which are still continuing, into the authorities' refusal to allow Orangemen in the town to walk along the Catholic Garvaghy Road.
The constable was married to a Protestant and had three young children. He was described by RUC Chief Constable Ronnie Flanagan as a dedicated public servant and community officer.
Mr Flanagan added: "Frank O'Reilly was an outstanding colleague who ran a young boys' football club in Portadown. He is a tremendous loss to the RUC, the community and most of all a tremendous loss to his family."
In a reference to the organiser of the protests, Mr Flanagan went on: "These people have no place in our society. They are not worth consideration. They are not loyalists - they are not deserving of any title.
"We have people here who bring others on to the streets, who say that they've no responsibility for what takes place thereafter, and there are people all too willing to engage in the kind of indiscriminate attacks that have cut Frank O'Reilly down."
The Orange Order in Portadown described the death as tragic but insisted its protests would continue. David Jones, a leading Orangeman, said: "Unfortunately when you are standing up for liberties sometimes the cost of those liberties can be very high for that. We don't continue the protest lightly but our protest will go on."
The RUC man's death brings to four the number of people killed during violence linked to the Drumcree protest. At the height of the stand-off in July, three young Catholic brothers perished in their beds during an arson attack on their home in Ballymoney, Co Antrim.
Irish Prime Minister Bertie Ahern said those responsible for the death of Mr O'Reilly should "hang their heads in shame".
The Democratic Unionist Party leader, the Rev Ian Paisley, who visited the injured man in hospital, said: "Nothing can justify such a heinous and damnable crime."
The Ulster Unionist leader, David Trimble, said: "This is a dastardly murder of a brave young officer who was doing his duty in Portadown protecting people and their property. It is a reflection of the problem that we have. It is a clear warning about how even peaceful protests can be exploited by evil people "
Anger over arms, page 10