"Good morning," the sharply dressed musician said to waiting reporters before heading into the closed-door hearing, where it is believed arrangements are being discussed prior to the full court case.
His wife, former model Heather Mills, arrived a short time earlier pulling a case containing legal documents for the case, which the couple have struggled to keep from turning bitter.
Divorce cases heard in the Queen's Building, a nondescript 1960s annexe to the Victorian Gothic spires and marbled halls of the main Royal Courts of Justice building, are invariably listed with the parties' surnames.
But the McCartney/Mills hearing before High Court Family Division judge Hugh Bennett was listed just as "Case", with the number FD06D03721.
Sir Paul, 64, dressed in a dark grey suit with black trainers, white shirt and white-spotted maroon tie, left the court after about one hour, giving a two-fingered salute.
Journalists speculated as to whether it was a "V for victory" or for peace.
About 30 minutes later, Ms Mills - dressed in a camel-coloured dress, black boots, a grey coat and sunglasses - left courtroom number 47 using an exit normally reserved for judges at the back of the building.
The 39-year-old, her blonde hair scraped back, said nothing as she stepped into the front seat of a black car before being driven out of the court's rear exit as photographers clamoured to take her picture.
Sir Paul had also left by the same exit, accompanied by his lawyer Fiona Shackleton, and drove off in a black four-wheel drive.
The couple, who have a three-year-old daughter, Beatrice, had unexpectedly both appeared in court for the initial hearings.
Ms Shackleton and Ms Mills' lawyer Anthony Julius represented Princess Diana and Prince Charles in their high-profile 1998 divorce.
Under British law, the press and public are barred from attending divorce case hearings. None of the lawyers involved would confirm the hearing had finished, but the legal documents were removed from the courtroom.
A joint statement issued later by the couple's lawyers urged against misreporting of the case in the media and appealed for them to be given space during the case.
"The parties both ask the media please to respect their privacy and the confidentiality of the proceedings, as they work to settle the outstanding issues between them in their divorce," it said.
Ms Mills and the former Beatle announced the end of their four-year marriage last May.
But the divorce has turned into an acrimonious affair played out in the media, with leaked divorce papers in November claiming Sir Paul mistreated his second wife.
One press report last month said he was planning to offer a £25 million ($62m) settlement to his estranged wife to end the bitter divorce battle.
Citing various unnamed sources, the tabloid said Sir Paul had instructed his legal team to make the offer to avoid a public and messy court case.