Iran has been a key supporter of the Houthi movement in Yemen, providing military, financial, and logistical support, despite both Iran and the Houthis denying the scale of assistance for years. The relationship dates back to the 1990s, when Houthi leaders received religious training in Iran. By 2009, Iran began offering more direct support, and this escalated after the collapse of the Yemeni government in 2011. Following the Houthis' takeover of Sana'a in 2014, Iranian support became more overt, with the supply of advanced weapons, military training, and intelligence. This support helped the Houthis bolster their military capabilities, including the use of sophisticated missiles and drones, which have played a significant role in their ongoing conflict with Saudi-led forces and with Israel, and with the disruption of the global maritime trade route through the Bab al-Mandab strait.

The strategic benefits for Iran in backing the Houthis are significant, particularly in terms of countering Saudi influence and furthering its regional interests. Iran has used the Houthis to destabilise the region and exert pressure on Saudi Arabia, including through attacks on Saudi military targets and commercial vessels in the Red Sea. This proxy warfare allows Iran to challenge Saudi Arabia without direct involvement. In return, the Houthis align themselves with Iran's ideological goals, promoting resistance against Western influence and supporting Iranian interests in the broader Middle East. However, the degree of Iranian control over the Houthis has also been exaggerated by anti-Houthi forces, such as subsequent Yemeni governments and their Saudi and American allies.

There is circumstantial evidence pointing to an informal relationship between Iran and the Houthis during the 1990s, as members of the al-Houthi family, Badr al-Din al-Houthi, and his sons, Hussein al-Houthi and Abdul Malik al-Houthi received religious training in the Iranian Islamic seminary in al-Qom. Prior to 2010, Iranian media denied Iranian assistance to the Houthis and rarely referred to the military and political crisis in Yemen, though from late November 2009 it gradually increased its reports of Saudi attacks against Yemeni Shi'ites, and at times portraying it as being against the entire Shia world. This is interpreted by the RAND institute as an attempt to garner public support for future Iranian assistance to the Houthis. According to some experts, Iran "has unquestionably lent the Houthis some support, most likely through its Lebanese proxy Hezbollah, since at least the mid-2000s", others assert that official Iranian influence on the Houthis began in 2009, with the final phase of the Houthi insurgency against the Yemeni government, when according to the Yemeni chief of counterterrorism, Iran was training and arming Houthi militants. Until the Arab Spring and the fall of the Yemeni government "the Yemeni state was weak but functional" and it was too difficult for Iran to infiltrate, but after 2011 the state nearly collapsed and the barriers preventing Iran's entry, which were maintained by the recognised Yemeni government, were eliminated. Newly opened smuggling routes between Iran and Yemen greatly limited the costs and risks involved in Iran's provision of materiel support to the Houthis.

Between 2011, when the revolt against the government began, and 2014, when the government was overthrown, Iranian support of the Houthis was fairly limited. In September 2014 the Houthis gained control over Sana'a, after which they began making several overtures to Iran, by releasing Iranian prisoners, both from Hezbollah and the IRGC, and by announcing direct flights from Iran to the airport in Sana'a, each act being an expression of Houthi aspirations for stronger ties and additional support from Iran. Most experts agree that Iran provided the Houthis with weapons that same year. By waging a civil war with Iranian assistance and pushing all the way to southern Yemen, the Houthis demonstrated their potential value to Iran. The Houthis view themselves as part of the "axis of resistance" led by Iran and their ideology is echoed in their slogans calling for the deaths of America and Israel, the cursing of the Jews and victory of Islam.

Iranian backing of the Houthis has been reported by diplomatic correspondents of major news outlets, and has been the reported perspective of Yemeni governmental leaders militarily and politically opposing Houthi efforts (e.g., as of 2017, the UN-recognized, deposed Yemeni President Abd Rabbu Mansour Hadi, who referred to the "Houthi rebels... as 'Iranian militias'"). The Houthis in turn accused the Saleh government of being backed by Saudi Arabia and of using Al-Qaeda to repress them. Under the next President Hadi, Gulf Arab states accused Iran of backing the Houthis financially and militarily, though Iran denied this, and they were themselves backers of President Hadi. Despite confirming statements by Iranian and Yemeni officials in regards to Iranian support in the form of trainers, weaponry, and money, the Houthis denied reception of substantial financial or arm support from Iran.

Some of Iran's regional interests and geopolitical objectives are served through its fostering of conflict and instability in Yemen, specifically along the border with Saudi Arabia, a long time adversary of Iran. Deployment of the Houthis along the border allows the crossing of terrorists into Saudi Arabia, and forces the Saudi Arabian military to focus on Yemen as opposed to Iran. By subsidising proxy warfare in the region Iran achieves its objective of threatening Saudi Arabia at a relatively low cost and minimal risk, but at a great expense for the Saudi military. Essentially, from that perspective, Iran is backing the Houthis to fight against a Saudi-led coalition of Gulf States whose aim is to maintain control of Yemen. Beginning in April 2015, the Houthis engaged in frequent assaults on Saudi Arabia, including ambushing of military convoys, overrunning small border forts, seizure and demolition of large Saudi facilities and partial occupation of depopulated towns, as well as multiple missile attacks involving short, medium and long range ballistic missiles. Additionally, Houthi controlled areas serve as a platform for an Iranian intelligence outpost and a covert weapons distribution network which would promote Iranian objectives in the Middle East and the Horn of Africa.

In return for the support they receive from Iran, the Houthis, as part of the "axis of resistance" seek to prevent Western influence on the Middle East and to intimidate the regional countries which ally themselves with the US. Iran expert Mohammad Ayatollahi Tabaar from Foreign Affairs states that the Houthis assist Iran by posing a regional threat to Saudi Arabia and allowing Iran to evade the sanctions on its oil trade by protecting the Iranian vessels in the Red Sea.

Conversely, different sources have also stated that the degree of Iranian control over the Houthi movement should not be exaggerated. In April 2015, United States National Security Council spokesperson Bernadette Meehan remarked that "It remains our assessment that Iran does not exert command and control over the Houthis in Yemen". Joost Hiltermann wrote that Iran does not control the Houthis' decision-making as evidenced by Houthis' flat rejection of Iran's demand not to take over Sanaa in 2015. Thomas Juneau, writing in the journal International Affairs, states that even though Iran's support for Houthis has increased since 2014, it remains far too limited to have a significant impact in the balance of power in Yemen. The Quincy Institute for Responsible Statecraft argues that Teheran's influence over the movement has been "greatly exaggerated" by "the Saudis, their coalition partners (mainly the United Arab Emirates), and their [lobbyists] in Washington."