The Formula One racing driver wants to pop the question to the X Factor judge before their sixth anniversary, according to The Sun.
The high-profile couple celebrated their five-year anniversary this month with a romantic holiday to Capri, and Lewis has apparently given his strongest hint yet that he is ready to settle down.
Lewis, 28, has been quoted as saying that five years together was a "milestone" and added that he would love to propose in the not to distant future, saying "before we get to six years."
Nicole, 34, and Lewis have gone from strength to strength, and despite their hectic and conflicting work schedules, both make time to see each other.
The former Pussycat Doll singer travelled to Monaco to support Lewis for the country's annual Grand Prix in May, and also supported him trackside at the Malaysian Grand Prix in March.
The couple began dating after meeting at the MTV Europe Awards in Munich in 2007. They briefly split in 2010 saying in a joint statement that they wanted to "focus fully on their careers". They soon reconciled in 2011 before splitting up again, but rekindled their romance January last year.