Fox has faced a drawn-out review since making the bid for Sky in December 2016 tied to concerns that Murdoch, who owns several United Kingdom newspapers, would gain too much control over the country's media.
Comcast said it would establish a separate board for Sky News and guarantee a decade of spending at equal levels to last year's.
Comcast, the owner of NBC and Universal Pictures, said it was delighted to be formalising its offer.
The cable giant on Wednesday made official a $31 billion bid for Sky, topping Fox's offer.
Notes the Wall Street Journal this morning: "Separately, Comcast is weighing whether to play interloper on the pending Walt Disney Co. acquisition of 21st Century Fox's entertainment assets, people familiar with the situation say". (FOX, FOXA) on 15 December 2016 and is now terminating the Co-operation Agreement entered into with Twenty-First Century Fox on the same date.
Although this may have started a bidding war, Sky was quick to respond to the announcement of Comcast's offer.
Sky, which had agreed to a takeover by 21CF, has now ended that pact because of the superior Comcast offer. The bid represents a 16 percent premium to the current offer from 21st Century Fox.
In its official offer for Sky, Comcast didn't change the terms of its informal offer, which it first disclosed in February.
The rival bid comes just ahead of a May 1 deadline for the Competition and Markets Authority (CMA) to give its final advice on the Fox bid for Sky to Culture Secretary Matt Hancock, who must decide to either approve or block it by the end of May.
Salmon said: "Part of the reason the value of the deal is significantly higher than what Fox originally put forward is that Sky has since secured three more years of rights to Premier League football at a reduced cost".
In the continuing saga of USA media conglomerates battling over Sky of the United Kingdom, Comcast has fired the latest salvo in its hopes of gaining control of the company.
The Fox offer had faced hurdles a year ago when the UK's Secretary of State for Culture, Media and Sport issued a European intervention notice, which asked United Kingdom media regulator Ofcom to report on two public interest considerations around the merger plans.
Sky's independent directors welcomed Comcast's 12.50 pound per share bid and said they would now engage with both Comcast and Fox.
That undertaking was anticipated to ameliorate any concerns over plurality, although the Fox-Disney deal remains under the scrutiny of United States regulators.
Rupert Murdoch, executive chairman of News Corporation.
Comcast sees Sky's 23M customers in the UK, Italy and Germany as a platform for further growth on the Continent.