Lady Mills McCartney, 38, has retained solicitor Anthony Julius, who acted for Princess Diana in 1996, winning a reported £17m settlement.
Sir Paul, 64, has chosen Fiona Shackleton, who represented Prince Charles, to argue his case.
The couple announced their separation in May after four years of marriage.
Their legal teams will be battling over Sir Paul’s fortune, which is believed to be more than £800m.
The couple, who have a two-year-old daughter, Beatrice, blamed their break-up on press intrusion, and said they remained friends.
But a spokesperson for Lady Mills McCartney said on Tuesday that Sir Paul had frozen their joint bank account and had complained about her removing three bottles of cleaning fluid from his home in Sussex.
Police were called to Sir Paul’s London home on Monday after an incident involving his estranged wife.