On 11 April 2018, as the SNP's Defence Spokesperson, McDonald warned Prime Minister Theresa May over launching airstrikes on Syria (in response to the Assad regime's chemical attack on civilians) without first having the airstrikes approved by a parliamentary vote. He said the SNP would support such airstrikes if they were part of a wider plan to bring an end to the war. The UK launched airstrikes on 14 April without a parliamentary vote, which McDonald condemned as "gesture bombing".