Justin Welby has described the attack on former spy Sergei Skripal in Salisbury as a "terrible event" and said those responsible should be "held accountable".
The Archbishop of Canterbury told ITV News that the fact chemical weapons are outlawed meant their illegal use was "wrong under all circumstances".
In a wide-ranging interview, he also warned about the devastating impact of prolonged austerity on UK society and spoke of the Church's need for reform following its sex abuse scandal.
The Archbishop also touched on his nerves ahead of the upcoming royal wedding between Prince Harry and Meghan Markle.
Mr Welby's comments follow the publication of his new book, Reimagining Britain: Foundations For Hope, which deals with both Brexit and society.
- Salisbury attack a 'terrible event'
Mr Welby was highly critical of the use of a nerve agent in Wiltshire, describing the attack on Mr Skripal and his daughter Yulia as "a sin".
But he urged the Government not to react out of fear and terror, saying that it could lead to wrong decisions.
"Chemical weapons are banned by international law, they are so awful that the whole world has got together and said 'you do not use these things,'" he said.
"So to use them, in any way, is completely wrong under all circumstances."
Speaking of increasing tensions between the UK and Russia, Mr Welby added: "I think it's a time for courage, for resilience and hope, for trust in God and to pray.
"We pray for all involved. But we mustn't react out of fear and terror because when you do that you do the wrong thing."
- Austerity 'deeply damaging' for weakest in society
Mr Welby told ITV News he was concerned about the Government's policy on austerity, saying that it focussed too heavily on those at the bottom of society.
Accepting the necessity of such a measure, the Archbishop said that the rich needed to bear a bigger burden than the poor.
"Austerity, when you look at its consequences, has been deeply damaging for the weakest in society," he said.
"At the heart of Christian teaching... is the concept of the common good, so austerity may be necessary but the way it's done must take into account the common good.
"The load must be borne most heavily by those with the deepest pockets and the greatest strength."
- Church 'needs to reform' after sex abuse scandals
Mr Welby admitted that the church needed to regain people's trust following years of clergy sex abuse scandals.
The church, which is currently witness to the independent inquiry into child abuse, has found its standing "deeply damaged," the Archbishop said.
He called on the church to "re-imagine" itself and prevent further sexual misconduct from happening again, saying that perpetrators had "betrayed" victims.
"The way we deal with that is so important because we have to be transparent and honest, not to cover up, not to pretend it's any less bad than it is," Mr Welby said.
"We have to take steps to ensure it's stopped and changed."
He added: "The church is in the middle of reimagining itself... and we will go on with that.
"We have to reimagine our role, our position, how we communicate the good news of Jesus Christ, how we live in a way that is convincing."
- Archbishop admits to nerves ahead of royal wedding
A week on from presiding over Ms Markle's baptism into the Church of England, Mr Welby described the ceremony as "very special" and "beautiful".
The Archbishop said he was preparing alongside Prince Harry and Ms Markle for their May wedding at Windsor Castle.
But he spoke of fears over dropping the ring, which he admitted he had done at a previous wedding.
Speaking of having the world's attention on him, Mr Welby said: "I'm really trying not to think of that too much.
"You focus on the couple. It's their day. At the heart of it are two people who have fallen in love with each other who are committing their lives to each other with the most beautiful words and profound thoughts in the presence of God."
He added: "You seek to do it in a way that respect their integrity and honours their commitment."