Bains, 36, has progressed to the No.2 role after three-and-a-half years as the Saints' general manager - player list and legal affairs.
A key member of the club's recruiting team during that period, he will relinquish those duties with the club believed to be looking into its recruiting structure.
It is understood he will retain list management responsibilities, controlling player contracts and the Saints' salary cap while also overseeing projects such as the Moorabbin redevelopment and push into New Zealand.
"I certainly have strong ambitions over time to take on more senior roles within a football club," Bains recently told AFL.com.au.
"I think in terms of my corporate background I've got a variety of skills that over time would be beneficial in other parts of the organisation.
"I've been very fortunate with the opportunities I've got at St Kilda to date and continue to get."
Finnis, who was appointed in March and started in his role in mid April, has been quick to restructure St Kilda's administration.
Weeks after arriving at the club the former AFL Players' Association boss cut the roles of chief operating officer Terry Dillon and general manager of commercial operations Shane Wakelin.
To replace the two positions, Finnis hired Christine Finnegan from the Melbourne Rebels, who he had worked with previously at the AFLPA.
The club also appointed New Zealand-based director Liz Dawson to its board last month, strengthening the club's Trans-Tasman strategy.
The Saints conducted a mid-year review of their football department in June, chaired by head of football Chris Pelchen.
It is believed the recommendations included an additional staff member in each of the areas of player welfare, psychology, development and recruiting.
