Though far from unexpected, his decision not to seek a fifth six-year term dismayed a party still struggling to adjust to its minority status on Capitol Hill and whose goal is less to regain control of the Senate than to prevent the Republicans next year increasing their 53 seats to a filibuster-proof majority of 60.
Speaking at the state Capitol in Atlanta where his political career began in 1968, Mr Nunn said he was seeking "more freedom, more flexibility" for his career, and emphasised he was not bowing out of the public arena - he has been touted as a possible Secretary of State should Bill Clinton win a second term.
Clearly, he was frustrated by the prospect of a long time in opposition, and by the shift to the left of the congressional Democratic party. Of the eight Democratic departures from the Senate next year so far announced, his will be the most damaging to party morale.
Like Senator Bill Bradley of New Jersey, who declared in August that he was stepping down, Mr Nunn is a pragmatic centrist, ready if necessary to go against the party line and an authoritative figure on both sides of the aisle. Such is his prestige that even Republicans on the Senate Armed Services Committee, which he used to chair, are said privately to have implored him to stay.
Even more important, the Democrats will lose perhaps their most powerful bulwark in the South, increasingly a Republican preserve in congressional and presidential elections. Mr Nunn's move proved that Southern Democrats were "in full retreat," said Alphonse D'Amato of New York, head of the National Republican Senatorial Committee.
Republicans will have high hopes of the Nunn seat. Almost all the eight Democratic vacancies are vulnerable - but few more so than his in Georgia, seven of whose 11 Congressmen are Republican, including House Speaker Newt Gingrich, who could not resist a partisan shot yesterday: "For those who have listened carefully, the Democratic Party is not the vehicle for values outlined by Senator Nunn."