After taking over a company subsequently renamed Iliad, Xavier Niel launched in 1996 the 1st reversed directory Service on the Minitel. This Service is still responsible for 1 million euros of revenue per year for Iliad. Niel remains Iliad’s majority shareholder, holding 63.93% of the share capital.
In 1999, he created Free, a French Internet Service provider. The name came from the fact that modem access was really free, which caused some stir among other (non-free) French Internet providers, as well as it raised some questions about Free's Business model. In 2002, Free launched a broadband package at a low price (€29.99 per month), which became the benchmark in the market. At the same time, Free developed and launched the Freebox: the first triple-play multi-service box in France. The free modem Service had brought to the company a strong potential customers portfolio, many of them switching to the broadband for the sake of comfort.
On 28 May 2004, Xavier Niel was indicted and detained for a month for alleged procuring and misuse of company assets, which occurred in several sex shops in which he was a shareholder. On 30 August 2005, a Nolle prosequi was pronounced for the procuring part of his indictment, while on 13 October 2006, he was given a 2 years suspended prison sentence for the misuse of company assets.
In late 2010 Niel was a member of a group of Investors which acquired a controlling stake in the newspaper Le Monde.
In 2012, he created Free Mobile, which revolutionizes mobile telephony in France, with a 25 US$ plan, including unlimited voice calls, text and data (3G/4G).
In 2013, Niel created a school named 42, which is a free tech school with no teachers, no books, no tuition for 1000 people every year.
As of April 2018, his net worth is estimated at US$9.6 billion.