The 28-year-old will join yachting greats like Sir Francis Chichester and Sir Robin Knox-Johnston and continue a remarkable sailing career, which already has seen her notch up five medals at the last two Olympic Games.
She will have completed over 28,000 miles of non-stop sailing, often surviving on less than one hour's sleep a night, navigating her way through hurricane force storms and encountering icebergs along the way.
The extent to which her exploits have captured the imagination of the nation will be demonstrated as television channels take the rare step of interrupting programming to cut live to Ellen and her purpose-built, 75ft trimaran, B&Q, as they sail back into Falmouth after leaving on 28 November last year.
And with until 7.04am on Wednesday morning to complete the job, only the cruellest of luck could deny MacArthur her glory.
After crossing the line, she will sail the 80 or 90 miles to Falmouth. For the first time on her voyage, she will be joined by a shore crew to sail the boat and a doctor to give her an initial check. Thousands are expected to gather to welcome her back.
The time of 72 days 22 hours 54 minutes and 22 seconds, set last year by Francis Joyon, the French yachtsman, had seemed likely to stand for some time, so vulnerable are record attempts to adverse weather or equipment failure.
But MacArthur looks set to knock between 36 and 48 hours off that remarkable time, despite losing more than ten hours in the past two days after a drop in winds.
Knowing the lull was due, MacArthur said she was was forced "to take" on a storm with force eight gales and winds gusting up to 40 knots on Saturday night.
She said: "We had a few really big waves in the night. I was virtually thrown out of the bunk by one that broke right over the boat and filled the cockpit. There must have been a ton of water in the cockpit, I was a bit worried."
With that drama passed, MacArthur was greeted today by 200-strong crew of the Royal Navy warship HMS Liverpool, who waved Union flags and ensigns as they passed her in the mid-Atlantic.
It was not the first time she has been cheered on by the armed forces: five Royal Navy ships have diverted to rendezvous with B&Q in the past two months, and RAF fighters buzzed her yacht as she passed the Falkland Islands.Reuse content