He was chairman of Islamic jurisprudence in the College of Sharia at Damascus University, and a signatory to the Amman Message and A Common Word documents.
Dr. Zuhayli also taught the principles of Islamic legal writing and evidence for graduate students in Sudan, Pakistan, and elsewhere.
Dr. Zuhayli's erudite understanding of Islamic law caused him to be chosen to design the curriculum of Damascus University's College of Sharia in the late 1960s.
Many of Dr. Zuhayli's opinions were seen as very moderate – including his support for what he called Islamic democracy, human rights, and freedom.
His works on Islamic legal theory establish that traditional Sunni Islamic orthodoxy is defined by that which complies to one of the four valid Sunni madhhab, however he also stated that following one of the four madhhab is not obligatory – what is religiously obligatory is for the layman, defined as one who has not achieved the ability of independent legal reasoning, is to follow a competent valid orthodox Mufti.
[6] Zuhayli's position on celebrating Muhammad's birthday or mawlid was that it is permitted and even encouraged as long as it is not believed to be a religious obligation or an act of worship and is free of sin.
In many ways he was critical of what he saw as heretical innovation (bid'ah) and even in some cases what he considered disbelief (kufr) committed by some Sufi groups which he called "unaccepted" and "blameworthy" such as calling upon pious saints or Muhammad to answer one's prayer – believing such possessed omnipotence or power independent of God,[8] which has caused him to be derided by some as being Wahhabi influenced or at least as a modernist .
However, al-Zuhayli has defended the practice of beseeching God through the intercession of the Islamic prophets and saints (tawassul) saying this has been "absolutely permitted by the people of the sunnah, whether in life or after death, by many proofs from our scholars who wrote about it in the books of theology and jurisprudence.
With deep regret, drums and horns have entered into our mosques during mawlid ceremonies, and this is what many scholars had called deviant and without sound foundation (in Islamic law), and this is my position.
In a scholarly article presented in 2005 to the International Committee of the Red Cross entitled Islam and International Law al-Zuhayli argued that the basis between Muslims and non-Muslim countries under Islamic law is one of peace and not war, and that war must be avoided and a last resort to be considered jus ad bellum.
He also argued that war must never be waged to force non-Muslims to convert to Islam or for account of their religion, but only in relation to aggression.
He bewailed the thesis of Samuel P. Huntington relating to the clash of civilizations and instead affirmed that the Qur'an praises the diversity of humanity.