SIG head of open architecture Steve Kowal and head of investment research Tom Berger are also leaving the company.
The departures are understood to be part of a round of cost cutting measures at the business.
Tomlins (pictured) will remain at the firm until around June, working on the integration of shared services such as IT, finance, customer services and investment administration into the UK business.
Once this completes he has agreed to leave the firm.
As the finance function is integrated, Lloyd has also agreed to leave the business early next year and his responsibilities will transfer to Phil Hine, currently finance director of shared services.
Mann has been responsible for the integration of Selestia, the development of the new Skandia Investment Solutions platform and the migration of Skandia Multifunds to SIS. This work has now been completed, so his role will not be replaced.
In November Skandia revealed that it was proposing to close nine regional adviser support offices and 100 sales staff are likely to face redundancy as a result of a review of the support the firm provides advisers.
Lloyd has been at the insurer for nearly seven years and Mann has been at the business for more than 12 years.