The latest site, in New Hedges village, Pembrokeshire, was acquired from an independent operator and has since been refurbished.
McColl's floated on the stock market in February this year at 191p per share which valued the company at £200 million, below an initial £225 million expectation.
Its shares fell 2.25, or 1.3 per cent yesterday to 169.75p to leave them well adrift of that flotation price.
James Lancaster, chairman and chief executive of McColl's Retail Group, said the group is focused on growing its estate.
He said: "This [750th store] is an exciting milestone for the group as we continue to expand our UK convenience store footprint and build on the success of our IPO earlier this year.
"We are continuing to respond to the needs of our customers by improving and extending the range of products and services we offer and our store expansion and conversion plan remains on track.
"We are delighted to have opened in New Hedges village and look forward to providing an excellent service to our customers there."
McColl's has been upgrading many of its newsagents into food and wine outlets in recent years while also overhauling its existing convenience stores. In addition to its 750 convenience stores it has 540 newsagents around the UK.
Around 150 of those shops are in Scotland with the newsagents typically under the traditional RS McColl brand which can trace its roots back to 1901.
The group has said it plans to have 1000 convenience stores and 340 newsagents before the close of 2016.
Its newsagents operate under the Martin's banner in England and Wales.
Revenue at McColl's Retail Group in the 12 months to the end of November in 2012 was said to be up 2.9 per cent, from £844.7 million to £869.4 million.
Underlying operating profit rose from £21.3 million to £23.3 million.