The two countries took their present form after the Sykes–Picot Agreement to dismember the Ottoman Empire into British and French spheres of influence after World War I.

The Ba'ath Party started in Syria, from which the Iraqi version emerged, and both produced diverging but nonetheless disastrous authoritarian regimes and dictatorships.

[4] The two countries were part of the Russia–Syria–Iran–Iraq coalition which was formed as a consequence of an agreement reached at the end of September 2015 between Russia, Iran, Iraq and the Syrian government to "help and cooperate in collecting information about the Islamic State to combat the advances of the group, according to the statement issued by the Iraqi Joint Operations Command.

[5][6][7] From 2017 to 2019, private militias in Iraq joined the Syrian Civil War on behalf of the Assad regime and helped eliminate the Islamic State within the country.

In April 1920, the Allied San Remo Conference was held in Italy, which announced imposition of the British mandate over Iraq and the French over Syria.

Although establishing unity between Iraq and the United Arab Republic was one of the goals of the Iraqi revolution, this did not happen, but the countries entered into a state of hostility and media attacks continued even after the separation of Syria from Egypt in 1961.

[14] By October 1978, Iraq President, Ahmed Hassan al-Bakr began working closely with Assad to foil the Camp David Accords; signing in Baghdad a charter for Joint National Action which provided for the "closest form of unity ties" including "complete military unity" as well as "economic, political and cultural unification".

[14] In 1978 Iraqi President Ahmed Hassan al-Bakr and Hafez al-Assad, had agreed to a plan and started to make treaties that would lead to the unification of Iraq and Syria.

The unity talks were eventually suspended indefinitely after an alleged discovery of a Syrian plot to overthrow Saddam Hussein in November 1979.

[14] Shortly after coming to power Saddam claimed to have been informed of a plot against him, supported by the Syrians, and suspended, then later abandoned the plan for unification.

Relations with Syria have been marred by traditional rivalry for pre-eminence in Arab affairs, allegations of involvement in each other's internal politics, and disputes over the waters of Euphrates River, oil transit fees, and stances toward Israel.

[25] Although some of Iraq's Shiite clerics refused to give support to Assad, and Muqtada al-Sadr called on the Syrian president to step down from power,[26] Iraq remains one of the few remaining Arab countries which support the Syrian government, and has abstained from voting to expel Syria from the Arab league.

[27] Both countries have closely cooperated with each other against the Islamic State, with Iraq being a part of the Russia–Syria–Iran–Iraq coalition which was formed as a consequence of an agreement reached at the end of September 2015 between Russia, Iran, Iraq and Syria to "help and cooperate in collecting information about the terrorist Daesh group (ISIL) to combat the advances of the group, according to the statement issued by the Iraqi Joint Operations Command.

[30] A vital border crossing near the town of Al-Qaim that links the capitals of Iraq and Syria, was re-opened on 30 September 2019, after being seized by ISIS jihadists since 2014.

[31] During the 2024 fall of the Assad regime in Syria led by Hay'at Tahrir al-Sham (HTS), Iraq and Shia PMF militias opted not to send troops to the country.

[32] Around 2,000 soldiers linked to Assad militias entered Iraq with the country's permission seeking refuge immediately prior to the fall of Damascus, bringing tanks and military equipment with them.

[33][34] On December 26, 2024, Iraqi Intelligence Chief Hamid Al-Shatri met with Ahmed al-Sharaa, leader of HTS, in Damascus, marking Iraq's first official contact with Syria's new administration post-Assad.

Discussions focused on security and stability along their 600 kilometres (370 mi) border, emphasizing the need to prevent ISIS armed groups from exploiting the situation.