Dr Edward Haughey was one of Northern Ireland's richest men and founded the world-renowned Norbrook Laboratories, which specialises in veterinary medicines and employs more than 1,000 people in Newry.
The 70-year-old died after his helicopter crashed in Norfolk on Thursday evening.
Prime Minister David Cameron paid tribute to his "good friend".
He said: "Lord Ballyedmond was a towering figure in Northern Irish business life, and passionate about peace and good relations north and south, east and west.
"He was a larger than life figure who was a great supporter of the Conservative party and a good friend to me."
On Friday Norbrook Laboratories flew the company flag at half-mast at the Co Down base.
A statement from Norbrook said: "It is with sincere sadness and deep regret that the company confirms our founding Chairman and CEO, Lord Ballyedmond, was one of four people who tragically lost their lives in an aviation accident."
The other victims were colleague and site foreman Declan Small, who was from Mayobridge in Co Down, and two pilots named as Captain Carl Dickerson and Captain Lee Hoyle.
"Our thoughts are with the immediate families and friends of the deceased who have requested privacy at this difficult time," Norbrook said.
The privately-owned Agusta Westland AW139 aircraft came down in thick fog in a field near a stately home belonging to Lord Ballyedmond.
Norfolk police were deployed to the scene in Gillingham, near Beccles, at 7.30pm after members of the public heard the noise of a loud crash.
They said all four occupants on board the aircraft were pronounced dead at the scene.
We take enormous pride in our Chairman’s extraordinary legacy in establishing Norbrook as a global veterinary and pharmaceutical industry leader.
Paying tribute to the top businessman, Norbrook said: "Management will continue to advance his pioneering vision with a renewed vigor and determination befitting his memory."
On Friday police said that forensic examinations were being carried out and a significant cordon remained in place due to the considerable size of the crash scene.
Superintendent Dave Marshall said police and emergency services were working towards the dignified removal of the bodies.
Earlier, Chief Superintendent Bob Scully passed on condolences to the family and friends of those who died on behalf of Norfolk police, while the PSNI confirmed they had received report of the crash.
It has emerged that Lord Ballyedmond had raised safety concerns with the Italian manufacturer of the aircraft.
A spokesperson for Agusta Westland said: "Obviously we are very much regretful of what happened and will support the ongoing investigation in any possible way."
As a result of his vision and leadership he created employment opportunities for many people in Northern Ireland.
First Minister Peter Robinson
First Minister Peter Robinson and deputy First Minister Martin McGuinness paid tribute to Lord Ballyedmond from America.
"Dr Edward Haughey was a great ambassador for Northern Ireland. He worked tirelessly to develop the globally respected Newry based veterinary pharmaceutical company Norbrook Laboratories," Mr Robinson said.
"A seasoned and well respected politician, Edward's passing will be a great loss to his family and everyone in Northern Ireland. My thoughts and prayers are with the families affected by this very sad news."
Mr McGuinness added: "I offer my condolences to the family and friends of everyone who lost their lives in this helicopter accident in Norfolk.
"I know the passing of Eddie Haughey will be acutely felt in the Newry and wider Co Down area where his entrepreneurial spirit was a catalyst for economic development in the area.
"Eddie was a highly motivated man with immense business skills and my thoughts and prayers are with his family at this most difficult time."
Northern Ireland Secretary of State Theresa Villiers passed her sincere sympathies to the families of the victims of the crash.
"Lord Ballyedmond created many jobs and opportunities in Northern Ireland through his leadership of Norbrook Laboratories, as well as serving with distinction in the Irish Senate and later in the House of Lords," she said.
His loss will be felt by many across Northern Ireland including the business community.
Secretary of State Theresa Villiers
DUP Enterprise Minister Arlene Foster also expressed her condolences on the passing of the Dundalk-born entrepreneur.
"Norbrook Laboratories currently exports to more than 120 countries worldwide and Lord Ballyedmond worked tirelessly to promote Northern Ireland as an investment location," she said.
SDLP MP for South Down Margaret Ritchie said Lord Ballyedmond had made a major contribution to the local economy.
"I wish to offer my condolences on behalf of all of the people of south Down to his family and to the family of the other young man at this stage," she said.
UUP Lord Empey, who has known the family for over 25 years, also paid tribute.
"This tragic accident has cut short the life of a man who had still much to give. The family circle will be numbed by the tragedy. They are in our thoughts and prayers and I would like to offer the family, deepest sympathies from the Ulster Unionist Party."
Alliance Leader David Ford, said he was "deeply saddened" to hear of Lord Ballyedmond's death and passed on condolences on behalf of his party to the families involved.
He said: "This is desperately sad news, not just for his family but for everyone involved in Norbrook Laboratories. He made an enormous contribution to the Northern Ireland economy over the years and provided employment to a large number of people."
Lord Ballyedmond, who was made a UUP peer in 2004 before switching to the Conservative Party, was born in 1944.
His title came from Ballyedmond Castle, which he owned in Rostrevor.