D-Day veterans met for afternoon tea and a formal dinner at the mansion near Portsmouth which served as the allies' forward headquarters for the D-Day beach landing operations.
The visit is thought to be the largest meeting of surviving D-Day veterans this year, as some are not well enough to make the journey to Normandy for the 80th anniversary.
Many of the veterans will travel to Normandy on Tuesday morning, while others will remain in the UK to attend the national commemorative event in Portsmouth on Wednesday.
Southwick House is a Grade II-listed Georgian mansion house that was the nerve centre of D-Day.
Supreme Allied Commander General Dwight Eisenhower and Commander of the Allied Ground Forces General Bernard Montgomery made the monumental call to launch D-Day from Southwick House.
Veterans meet for tea in the Eisenhower Room, where the D-Day general gave the order to invade Normandy
Veterans gathered in what is now named the Eisenhower Room, where the fateful decision was made.
The veterans will be at the heart of commemorations to mark the 80th anniversary of the Normandy Landings this week.
The gathering at Southwick House began a week of commemorations in the UK and France.
The city of Portsmouth will host the Ministry of Defence's national commemorative event on Southsea Common on the morning of 5 June.
The event will be broadcast live on BBC One and BBC iPlayer and will feature appearances by members of the royal family, military musicians and a flypast by the Royal Air Force's Red Arrows.
The commemorations will continue in Normandy on Wednesday evening with a moving vigil and light show at the Commonwealth War Graves Commission's Bayeux War Cemetery.
Southwick House is still a working military base, and is home to the Defence School of Policing and Security.
On Thursday 6 June, the date of the 80th anniversary, the Ministry of Defence and the Royal British Legion will host the UK's national commemorative event at the British Normandy Memorial in Ver-sur-Mer, France.
Southwick House is still a working military base and is now home to the Defence School of Policing and Security.
