Soviet party chairman Leonid Brezhnev, left, Chancellor Willy Brandt and West German State Secretary Egon Bahr during a boat ride on the Black Sea in 1971. (Fritz Reiss/AP)

Egon Bahr, the German statesman who helped lead the Ostpolitik, or eastern policy, of improving relations with the communist East under West German Chancellor Willy Brandt, a reduction of tensions that eventually led to reunification, has died.

He was 93.

Social Democratic Party leader Sigmar Gabriel said Aug. 20 that Mr. Bahr died overnight. No cause was given.

“Egon Bahr’s work for Germany and Europe achieved historic significance even during his lifetime,” Gabriel said, adding that Mr. Bahr’s greatest reward was seeing the Berlin Wall come down in November 1989. Reunification followed the next year.

For decades, Mr. Bahr was not only an architect of West German foreign policy but a widely respected elder with personal ties to officials in the Soviet Union and East Germany, as well as in France and the United States. He became a frequently used back channel for German officials conducting political negotiations.

Egon Bahr, member of the German Social Democratic Party, delivers a speech next to a sculpture of former SPD leader and German Chancellor Willy Brandt in 2007. (Tobias Schwarz/Reuters)

But Mr. Bahr was frank and critical about his failure to understand how quickly and easily the Soviet bloc would fall in the revolutions of 1989. “To say there is any realistic chance of my country uniting is a lie,” he told The Washington Post four months before the Berlin Wall fell. “Our neighbors would never accept it, and I don’t know that we really want it.”

Even if the two German nations were to recombine, he said then, “I fear you would have to intervene eventually to save us from ourselves.”

Asked about those comments four years later, Mr. Bahr said he had been blinded by an overblown belief in the power and popular acceptance of the East German Communist regime, and by his own belief that the Nazi era rendered the Germans untrustworthy for generations to come.

“Because of what we had been through, I thought it was not possible for us to be a normal country so soon,” he said.

As a state secretary under Brandt, Mr. Bahr helped guide negotiations between divided East and West Germany, as well as with the Soviets, and played a key role in the negotiations of several treaties. He also served as minister for special affairs, then as minister for economic cooperation under Brandt’s successor, Helmut Schmidt.

German Foreign Minister Frank-Walter Steinmeier noted that Mr. Bahr was convinced that lasting peace in Europe wouldn’t be possible without Russia. The German News Agency reported that Mr. Bahr was in Moscow this past month campaigning for better relations between Germany and Russia. Ties between the two countries have been strained over Russia’s involvement in the Ukraine conflict.

Egon Karl-Heinz Bahr was born in Treffurt, Germany, on March 18, 1922. He was drafted into military service during World War II, but the discovery of his grandmother’s Jewish roots led to his expulsion from the Luftwaffe.

After the war, he worked for a German-language newspaper founded by the American occupation forces, a newspaper in West Berlin and as Bonn correspondent for the West Berlin radio station RIAS, or Radio in the American Sector.

Mr. Bahr joined the Social Democratic Party and was hired as press secretary to Brandt, then serving as West Berlin mayor, in 1960. He remained with Brandt after he became West German foreign minister in 1966 and became part of the politician’s “brain trust,” working on ways to alleviate the trauma of a divided capital and country.

He became a major voice on the need to foment change through contact rather than through confrontation. With Brandt, Mr. Bahr worked on practical efforts to bring together families on opposite sides of the Berlin Wall, such as treaties that allowed Christmastime visits to East Berlin.

When Brandt became West German chancellor in 1969, Mr. Bahr was given a portfolio that included negotiations with the Soviet foreign minister, Andrei Gromyko. The two Germans realized that the real power rested in Moscow and focused on reaching an accord there while also continuing talks with their East German counterparts. Brandt and Mr. Bahr succeeded in opening avenues of communication on trade and transportation between East and West Germany.

Brandt received the 1971 Nobel Peace Prize for his work. But he resigned as chancellor three years later after it was revealed that one of his aides was an East German spy. Mr. Bahr remained in government, serving as minister for economic cooperation in Schmidt’s cabinet for two years.

He then spent several years as general secretary of the Social Democratic Party, in which Brandt had retained his position as chairman. Mr. Bahr also became a member of the West German parliament and director of an institute for peace studies at the University of Hamburg.

He wrote on European security and published a volume of memoirs in the 1990s.

Survivors include his wife, Adelheid. A complete list of survivors was not available.

Marc Fisher contributed to this report.