He turned professional at the end of 2004 after completing Stage One of the European Tour Qualifying School, finishing eighth at the Finals at San Roque Golf Club where he secured his card for the 2005 season.

He finished runner-up at the 2009 Estoril Open de Portugal after losing in a playoff to Michael Hoey.

He finished second for the third straight week at the Ballantine's Championship, where he lost to Thongchai Jaidee in a 3-way playoff in extremely tough conditions in Korea.

Fernández-Castaño won his sixth career European Tour title in September 2012 at the BMW Italian Open.

[6] In early 2013, Fernández-Castaño played several events on the PGA Tour, finishing third in the Arnold Palmer Invitational on a sponsor's exemption and reaching the 27th place in the Official World Golf Ranking, his best to date.

[7] He also finished 10th in the U.S. Open, and concluded the season with more points than the 125th PGA Tour player to earn a place as a full member for 2014.

On the European Tour he won the BMW Masters and finished six times in the top-10, missing only one cut in 21 events;[8] he ended the season ranked 7th on the Race to Dubai, his best ever performance to date.