Mr Mockridge departed News International at the end of December after he missed out on the top job at New Corp's newly hived-off newspaper and book publishing arm.
His new role, subject to the completion of the Liberty Global takeover, expected in June, will see Mr Mockridge go head to head with the man he worked under for almost 22 years.
Liberty Global's $23.3bn (£15.75bn) acquisition of Virgin Media will make the US cable company, which already owns businesses in Germany, Belgium and Switzerland, one of the biggest pay-TV providers in Europe and a major rival to News Corp-controlled British Sky Broadcasting.
"I’m excited to become part of the Liberty Global family and look forward to working closely with Mike and his team as they continue to build the world’s largest cable platform,” said Mr Mockridge.
Although Virgin Media, with about 5m customers, still trails the market-leading BSkyB, which has 10.7m households signed up to its service, it is widely expected that efforts to steal market share will accelerate in the wake of the takeover, extending a longstanding rivalry between Liberty Global owner John Malone and Mr Murdoch.
The pair last locked horns a decade ago when they wrestled for control of America's biggest satellite broadcaster DirecTV.
Back then, Mr Malone managed to force Mr Murdoch to sell him the satellite network at a knockdown price after secretly amassing 19pc of New Corp's voting shares.
However Mike Fries, chief executive of Liberty Global, insisted that there would be any strategic overhaul at Virgin Media when it joins Mr Malone's stable.
"This is not a turnaround," he said. "We're acquiring a healthy, successful business and want to preserve the momentum the company already has."
In a statement announcing Mr Mockridge's appointment, Mr Fries said: “Tom will bring to Virgin Media a breadth of experience in the pay-TV industry, both in the UK and throughout Europe.
"We are fortunate to bring an executive of Tom’s talent and experience in to lead Virgin Media in its next phase of growth."
Mr Mockridge, who was parachuted in from News Corp's Sky Italia division to replace Rebekah Brooks as head of News International after she was unseated following the News of the World phone hacking scandal, spent 18 months steering the publishing group through the tumult that ensued.
He had been widely tipped to lead News Corp's new publishing arm, created by the splitting of Mr Murdoch's media empire, as reward, but was passed over for Wall Street Journal managing editor Robert Thomson.
Asked whether he felt apprehensive about taking on his former boss, the erstwhile News Corp veteran was keen to stress his view that "there is plenty of growth potential for Virgin, Sky and other operators" in the sector.
"I want to make sure I do not disrupt what Liberty and Virgin have already achieved," he added.
© Copyright of Telegraph Media Group Limited 2013.