The firm says the appointment is part of ongoing organisational changes that will also see the creation of three further roles, operations director, head of sales and adviser support manager.
Managing director Dave White says: “We continue to optimise the structure of the business to ensure the right people are in the right places as we head into our next phase of development.
“Mary will head up the new combined sales and marketing division, with the support of the new head of sales and the adviser support manager.
“These changes embody our focus on building stronger relationships with advisers, providing innovative solutions to their needs and delivering unrivalled levels of service and support.”
Stewart has been with Hornbuckle Mitchell for more than three years as marketing director and was appointed to a full member of the board last year.
Money Marketing revealed last month that Hornbuckle Mitchell director and head of sales for London Elaine Turtle was leaving the Sipp provider. Turtle is understood to be one of Hornbuckle’s top salespeople.
She is planning to travel for around a year before potentially looking for another role.