The couple were said to be on the rocks earlier this month after Field refused to leave Los Angeles to live in the UK with the popstar.
However, insiders have now claimed that the pair are determined to stay together, though Field will still spend much of her time working in the States.
A source close to Williams told The Mirror: "He seems the most content he has been in a long while. It wouldn't be a surprise if they announced an engagement, but not just yet."
Williams and Field reunited in October last year following a temporary split.