A native of Ashkirk, near Selkirk, Allan was born on 6 May 1971 to Christine and John H. Allan. He graduated from the University of Glasgow with an MA in Scottish Language and Literature, continuing his studies at the University of Aberdeen, graduating with a PhD in Scots language in 1998. He devoted his time and employment to the Scottish National Party in Peterhead, working for Alex Salmond MP, the now former First Minister of Scotland, and he subsequently became assistant to Michael Russell MSP. Allan was the SNP candidate for Gordon at the 2003 Scottish Parliament election. As National Secretary of the SNP, he was responsible in July 2004 for the expulsion of Campbell MartinMSP from the party after Martin had claimed that there was a case for supporters of independence not voting SNP. Previous to becoming an MSP, Alasdair was senior media relations officer for the Church of Scotland. Allan was next in line to become a list MSP for North East Scotland when Richard Lochhead resigned to fight the Moray by-election, however he decided instead to devote himself to contesting Na h-Eileanan an Iar, a key Labour–SNP marginal seat in the 2007 Scottish Parliament election. He relocated to Lewis and resigned his post as SNP National Secretary. This move proved successful, as he was elected with 46.6% of the vote – a 5.4% swing from Labour. In the 2011 Scottish Parliament General Election Allan again stood for the SNP in the now renamed seat of Na h-Eileanan an Iar and increased his majority, returning to Holyrood with 65.3% of the vote, an increase of 18.7% and a swing of 15.8% from Labour. As of July 2020, Allan is a member of the Committee on the Scottish Government Handling of Harassment Complaints, the Education and Skills Committee and the Justice Committee of the Scottish Parliament. He is a speaker and strong supporter of Scottish Gaelic and Scots and holds a PhD on the latter. He authored the booklet Talking Independence, which sought to answer questions about Scottish independence, ranging from "What will I pay in tax?" to "Will I still be able to visit relatives in England?" and "Will we still get EastEnders?". Allan voted against same-sex marriage in Scotland, saying he "favours the traditional definition of marriage" – in contrast to the position of the majority of the SNP government.
