The Republic of Ireland should consider rejoining the Commonwealth as Britain celebrates the Queen's Diamond Jubilee, said Tom Elliott, the leader of the Ulster Unionist Party.
Her visit to Dublin and Cork last year suggested a new relationship between the two states, he added.
Sinn Fein was the only party not to speak during a brief session at the Northern Ireland Assembly on Monday marking the monarch's 60th year on the throne.
Mr Elliott said the Queen's visit to the Republic of Ireland last year suggested a new relationship between two states that are "so close geographically but are maybe so apart in other circumstances".
"It may actually encourage the Republic of Ireland to look at the possibility to rejoin the Commonwealth once again," he added.
The Republic left the Commonwealth in 1949 and since then has sought to align itself to Europe, embracing the Common Market in a fashion aimed at reducing Ireland's reliance on Britain. The UK is still the country's major trade partner.
In May last year the Queen visited Ireland, the first British monarch to do so since independence in 1922.
She visited the garden of remembrance for Irish republican dead who took part in the 1916 Easter Rising against Britain in Dublin and expressed sympathy for those who suffered as a consequence of "our troubled past" during a keynote speech in the Irish capital.
She also toured Cork to a warm reception from local traders and customers.
Democratic Unionist party leader and First Minister Peter Robinson paid tribute.
"I am convinced that everyone in Northern Ireland will respect the significant role played by Her Majesty the Queen over such a significant period of time," he said.
"She has brought a wise head to difficult situations, always there to give sound counsel to those who have audiences with her."
While Sinn Fein abstained, in a silence described as "stony and churlish" by unionist MLA Jim Allister, the nationalist SDLP acknowledged the Queen's achievement.
SDLP leader Alasdair McDonnell said: "We all must recognise that our [image] of ourselves and of our future changes in time and we hope and believe that that is for the better.
"The visit of Queen Elizabeth the second to Dublin and the work of [Irish] president [Mary] McAleese was another important step forward in a process of reconciliation between the peoples of these islands."