Thompson, who owns Cheveley Park Stud along with husband David, famously bought the Nick Gaselee-trained Party Politics just days before the Aintree spectacular and she will be targeting similar success with her Paul Nicholls-trained recruit.
Le Mercurey finished second to the ill-fated Many Clouds over regulation fences at Aintree back in December and also chased home Native River in the Denman Chase, before most recently finishing third in his prep outing at Kelso.
Nicholls told his Betfair blog: "Mrs Thompson has been an owner here for some time and has done well with Boa Island this season.
"She was looking for a Grand National contender with solid form and Le Mercurey fits the bill.
"Mrs Thompson bought Party Politics a few days before he won the race in 1992 and I'm hoping she strikes lucky again.
"Le Mercurey has run really well several times this season including when narrowly beaten by Many Clouds at Aintree last December.
"He was ridden there by Sean Bowen who keeps the mount as Sam Twiston-Davies has chosen another of mine, Saphir Du Rheu, who finished a close fifth in the Gold Cup earlier this month."
Nicholls also has Wonderful Charm, Just A Par and Vicente in the National frame, and added: "All five of my National entries are in great form at home and they will all be suited by goodish ground on the day."