The West London side were always one of the forerunners to purchase the defender but took the pre-emptive stroke in making him their player by becoming the first club to agree a fee for his services.
It was always likely that the England international would be switching his allegiances in January after it emerged that Bolton were unlikely to tie the 26 year-old down to a contract extension at the Reebok Stadium and rather than lose him on a free transfer in the summer, would cash in on the star.
The Blue wasted no time in matching the £7m valuation of Cahill, submitting their bid as soon as the January transfer window opened, and after two weeks of negotiations – that were in doubt at one point due to a dispute over wages – Cahill has finally signed.
Other clubs in the frame to sign the centre-back were Manchester United, Tottenham and Arsenal who are all believed to be looking into signing a central defender.
Cahill was in attendance at Stamford Bridge over the weekend as Chelsea ran out a 1-0 victory over high-flying Sunderland, before penning his move on Monday.
The former Bolton Wanderer will be hoping to seal a starting berth at Chelsea alongside international compatriot John Terry as he attempts to tie down a spot in Fabio Capello’s England starting XI for Euro 2012.