Both current and future customers invested directly in M&G ISAs and funds will be eligible for the new service.
The ongoing charge figure for a typical M&G equity fund such as the M&G Dividend Fund, will fall 50bps to 1.16% for all direct customers with at least £5,000 in their portfolios.
The OCF for a typical M&G bond fund such as the M&G Corporate Bond Fund, will fall 25bps to 0.91%.
A direct investor with £2,500 in each of these two funds moving to the new online service would automatically transfer to 'R share classes' and see total annual charges fall by £18.75, for example.
Also, in a move similar to one made by Neil Woodford’s firm, M&G will stop charging investors for external research from 1 January 2017, with M&G picking up the tab itself.
Chief executive of M&G Investments Michael McLintock said: "The lower fund charges available through our new online service will help our customers' savings work as hard as possible, whether that's to provide an income in retirement today, or grow capital for the future."
Global head of retail sales Jonathan Willcocks added: “Lower transaction costs are great news for all our investors and I’m delighted that we’re also offering our direct customers a more modern, round the clock, execution-only service."