The couple, who share 1-year-old son August, are said by the Daily Telegraph to be splitting their time between the exclusive CostaTerra Golf and Ocean Club, south of Lisbon, as well as London.
Brooksbank, 36, is said to have got a new job with businessman Mike Meldrum, 54, a businessman who is a long-term friend if actor George Clooney, 61.
A source said: “Jack is now working for Mike Meldrum and they are splitting their time between Portugal and London.
“It’s a very exciting time for them.”
Brooksbank will work in sales, marketing and promotion for Meldrum’s private 300-house private resort, now under development.
Eugenie, 32, Jack and August had been living at Frogmore Cottage on the Windsor estate – still the UK home of Prince Harry and Meghan Markle, with the Princess carrying out her job at art gallery Hauser & Wirth on hybrid basis.
Harry, 37, and Meghan, 40, have renewed their lease on the cottage despite living in an $11 million (R170m) mansion in California.
Brooksbank previously worked for tequila brand Casamigos, which was jointly owned by Meldrum, Clooney and their friend Randy Gerber, 60 – married to supermodel Cindy Crawford, 56 – before it was bought by drinks giant Diageo for up to $1 billion.
Harry and Meghan had been expected to let their Frogmore Cottage lease expire after they quit the UK for America, but they have reportedly committed to a new 12-month rolling deal.
Royal insiders say the move could mean that the Sussexes plan to spend more time in Windsor.
One source said: “It is quite a signal that they aren’t going to disappear. They could easily give up Frogmore as their life’s now in California.
“By agreeing to extend the lease, and with Jack and Eugenie focusing on Portugal, they have a firm presence smack bang in the middle of the Windsor court where it’s all happening. They can now come and go any time they please.
“The coming year could be one of the most tumultuous in royal history and the Sussexes are making sure they have a foothold in Windsor.”
A Buckingham Palace spokesman said: “Frogmore Cottage remains the UK home of The Duke and Duchess of Sussex.”
The Queen is said to be planing to meet the couple’s daughter Lilibet for the first time this weekend during the monarch’s Platinum Jubilee celebrations, which will also see the pair bring their son Archie, 3, to Britain.