After leaving school at 16, Christodoulou trained to become a diamond mounter before acquiring his first property in 1994. He began his business career in Hatton Garden, persuading the landlord of a small jewelers to allow him to occupy a workshop by accepting cut-price jewellery repairs as a form of rental income. Within three years, Christodoulou had sold his own diamond business. Christodoulou then moved into the building trade by taking jobs on construction sites before developing his own buildings with generous bank finance.
He started at 19 with a studio flat in Finchley, north London, and now owns extensive property in London Docklands through his Yianis Group. With circa 2 million square foot of property, Christodoulou is the second largest freeholder in Canary Wharf after Canary Wharf Group, which is jointly owned by Canadian private equity firm Brookfield and the Qatar Investment Authority.
Christodoulou owns 100% of Yianis Group, which owns the London hotels Marriott Canary Wharf and the Canary Riverside Plaza (formerly Four Seasons Canary Wharf). He also owns heritage asset Wool House, a grade II listed former Victorian warehouse in Whitechapel. In 2019, it was reported that the Cyprus-born British freehold tycoon was working on an eco-friendly development on an island off Sardinia.
In 2012, several overleveraged hotel-owning Yianis Group interests that came under the Dania Properties name went into administration, which saw Christodoulou lose the grade 2-listed 148 bedroom hotel Marriott Victoria & Albert Hotel in Manchester and the four-AA-star, 895-bedroom Park Inn by Radisson located close to Heathrow Airport.
The value of Christodoulou's property holdings increased by 25% in the 12 months to April 2019 to £1.5 billion, due to a buoyant London rental market.
As of May 2022, his net worth is £2.35 billion, according to the Sunday Times Rich List 2022.
In October 2021, Christodoulou had been set to take over Cypriot professional football club Omonia Nicosia from current major stakeholder Stavros Papastavrou, a New York-based Cypriot investor, in a £30 million deal, but talks reportedly broke down over the issue of him having to sell the shares on to Omonia fans after five years, one of at least two clauses in the original management deal with Papastavrou that Christodoulou had sought to scrub.