Greer entered public life in the wake of the Great Irish Famine which, together with a drop in agricultural prices, compounded the poverty and insecurity of tenant farmers. Taking up the call for immediate rent reductions, and the protection of the Ulster custom of tenant right (which gave tenants a saleable interest in their holdings). in 1847 Greer joined James MacKnight, editor of the "Londonderry Standard," William Sharman Crawford MP, a progressive County Down landlord, and group of radical Presbyterian ministers in forming the Ulster Tenant Right Association.