Born in Poland, he came to Palestine in 1935. His family name was Jazernicki but he later changed it to Shamir. Shamir joined the Irgun Zvai Leumi, one of the underground Jewish militant organizations directed against the British occupation of Palestine. When the Irgun split in 1940, Shamir sided with the most militant faction, headed by Avraham Stern, which later became known as the Stern Gang. After Stern was killed by British in 1942, Shamir became one of the three leaders. During his tenure, the Stern Gang was responsible for many deeds, including the 1944 assassination of Britain's minister of state for the Middle East, Lord Moyne, and the 1948 assassination of the United Nations representative in the Middle East, Count Folke Bernadotte.
After the successful battle for independence, Shamir joined the secret intelligence service (Mossad) (1955-1965) and was first elected to the Knesset in 1973. He became chairman of the Knesset in 1977, and foreign minister in 1980, before succeeding Menachem Begin as prime minister in 1983.
Shamir had a reputation as a Likud hard-liner; he opposed the Camp David accords; he opposed the peace treaty with Egypt, and he opposed the Cabinet’s decision to withdraw the Israeli Army from Lebanon.
His failure to stabilize Israel's inflationary economy led to an indecisive election in 1984, after which a coalition was formed between his Likud Party and the Labor Party, led by Shimon Peres. Peres agreed to be prime minister until September 1986, when Shamir took over.
As he prepared to reclaim the office of prime minister, which he had held previously from October 1983 to September 1984, Shamir's hard-line image appeared to moderate. Reelected in 1988, Shamir and Peres formed a new coalition government until 1990, when the Labor party left the government, leaving Shamir with a narrow coalition.
In 1991 the Shamir government took part in the Madrid peace talks. The Shamir government also did not attack Iraq for firing volleys of Scud missiles at Israel. The United States urged restraint, saying Israeli attacks would pose problems for the delicate Arab-Western coalition assembled against Iraq. Although long a hard-liner, Shamir left office in 1992, after his government fell amid charges that Likud was too conciliatory toward the Palestinians, and was succeeded by Yitzhak Rabin.
Shamir stepped down form Likud leadership in March, 1993. He was a sharp critic of his Likud successor, Benjamin Netanyahu, as being too soft and indecisive in dealing with the Palestinians.