Schmidt resigned from the board late last year in anticipation of taking a job as chief executive of Louis Dreyfus Commodities.
However, a final agreement was never reached and Louis Dreyfus said earlier this month that both sides had agreed "not to proceed with the engagement" following a more detailed analysis of the terms and conditions of the appointment.
Schmidt has been appointed as a member of the audit committee and the human resources and compensation committee at Agrium.
Under his leadership, Schmidt led Viterra's evolution from a regional co-operative into a publicly traded international agribusiness until his departure in 2012.
Viterra was later purchased and taken private by Swiss commodities giant Glencore, while parts of the business were sold to Agrium and Richardson International.
Schmidt joined the board of Agrium in 2013.