Hezbollah involvement in the Syrian Civil War has been substantial since the beginning of armed insurgency phase of the Syrian Civil War in 2011, and evolved into active support for Ba'athist government forces and troop deployment from 2012 onwards. By 2014, Hezbollah was deployed across Syria. Hezbollah has also been very active in preventing Al-Nusra Front and Islamic State penetration into Lebanon, being one of the most active forces in the Syrian Civil War spillover in Lebanon.
In the past, Hezbollah has served a strategic arm of Iran in the region, playing a key role in the Iran–Israel and Iran–Saudi Arabia proxy conflicts. On a number of occasions, Hezbollah weapon convoys in Syria and Syrian-Lebanese border areas were attacked, presumably by the Israeli military. Hezbollah convoys and militant camps have also been attacked by various Syrian rebel factions.
Hezbollah's image in the Arab World - especially in Syria and Lebanon - has been greatly tarnished due to its sectarian activities throughout the course of the Syrian civil war. Major religious leaders and activists, Sunni and Shia alike, have condemned Hezbollah, with many former supporters of Hezbollah becoming its fervent opponents for its stance in Syria. Shi'i cleric Subhi al-Tufayli, the group's founder and principle architect during 1980s, fiercely denounced Hezbollah for abandoning its founding principles and accused it of serving the hegemonic ambitions of Iran and Russia.
Timeline of Hezbollah deployment in Syria
2011–2012
Hezbollah has long been an ally of the Ba'ath government of Syria, ruled by the Al-Assad family. Hezbollah has helped the Syrian Ba'ath government during the Syrian civil war in its fight against the Syrian opposition, which Hezbollah has described as a "plot to destroy its alliance with al-Assad against Israel". Geneive Abdo opined that Hezbollah's support for al-Assad in the Syrian war has "transformed" it from a group with "support among the Sunni for defeating Israel in a battle in 2006" into a "strictly Shia paramilitary force".
In August 2012, the United States sanctioned Hezbollah for its alleged role in the war. General Secretary Hassan Nasrallah denied Hezbollah had been fighting on behalf of the Syrian Ba'ath government, stating on 12 October 2012 that "right from the start the Syrian opposition has been telling the media that Hezbollah sent 3,000 fighters to Syria, which we have denied". However, according to the Lebanese Daily Star newspaper, Nasrallah said in the same speech that Hezbollah fighters helped the Ba'athist government "retain control of some 23 strategically located villages [in Syria] inhabited by Shiites of Lebanese citizenship". Nasrallah said that Hezbollah fighters died in Syria doing their "jihadist duties".
In 2012, Hezbollah fighters crossed the border from Lebanon and took over eight villages in the Al-Qusayr District of Syria. On 16–17 February 2013, Syrian opposition groups claimed that Hezbollah, backed by the Syrian military, attacked three neighboring Sunni villages controlled by the Free Syrian Army (FSA). An FSA spokesman said, "Hezbollah's invasion is the first of its kind in terms of organisation, planning and coordination with the Syrian regime's air force". Hezbollah said three Lebanese Shiites, "acting in self-defense", were killed in the clashes with the FSA. Lebanese security sources said that the three were Hezbollah members. In response, the FSA allegedly attacked two Hezbollah positions on 21 February; one in Syria and one in Lebanon. Five days later, it said it destroyed a convoy carrying Hezbollah fighters and Syrian officers to Lebanon, killing all the passengers.