The Court of Arbitration for Sport suspended the three-time Tour champion after rejecting his claim that his positive test for clenbuterol was caused by eating contaminated meat.
The three-man CAS panel upheld appeals by the International Cycling Union and World Anti-Doping Agency, which challenged a Spanish cycling tribunal's decision last year to exonerate Contador.
His ban was backdated and he is eligible to return to competition on Aug. 6.
The decision was announced by CAS in Lausanne, Switzerland.
Contador has continued racing since testing positive on a 2010 Tour rest day.
Contador becomes only the second Tour de France champion to be disqualified and stripped of victory for doping. The first was Floyd Landis, the American who lost his 2006 title after testing positive for testosterone.
Andy Schleck of Luxembourg, who finished second at the 2010 Tour, stands to be elevated to victory.
Contador tested positive on the July 21 rest day. The positive results were not confirmed publicly until September 2010, when the UCI announced it had provisionally suspended him pending an investigation by Spain's cycling body.
Contador blamed steak bought from a Basque producer for his high reading of clenbuterol, which is sometimes used by farmers to fatten up their livestock.
Contador was originally cleared last February by the Spanish cycling federation's tribunal, which rejected a recommendation to impose a one-year ban. Days earlier, then Spanish Prime Minister Jose Luis Rodriguez Zapatero said on Twitter that there was no reason to punish the rider, who is a sports icon in his home country.
After the UCI and WADA appealed the Spanish verdict, a twice-postponed hearing was eventually heard by CAS in November.
The four-day session almost ended in chaos as lawyers for the UCI and WADA considered walking out when the panel chairman, Israeli lawyer Efraim Barak, prevented one of their expert witnesses from being questioned about the science of blood doping and transfusions.
The complex 18-month legal case has also raised questions about the status of clenbuterol in anti-doping rules and the honesty of Spanish farmers. The drug is banned in Europe.
Contador is one of only five cyclists to win the three Grand Tours -- the Tour de France, the Giro and the Spanish Vuelta. He also won the Tour de France in 2007 and 2009.