Born in Bucharest, she trained in Kiev for seven years before joining the Royal Ballet School in 1997 on a Prix de Lausanne scholarship. Upon completion of her training, six months later, she returned to Kiev to dance with Kiev Ballet for a year. Her repertoire with Kiev Ballet included Don Quixote (Kitri), The Sleeping Beauty (Aurora, Princess Florine), Cinderella, The Nutcracker (Clara), Coppelia, (peasant pas de deux) and the Hungarian Dance in Swan Lake.
She joined the Royal Ballet in November 1999 and at the end of the season was promoted from Artist to First Soloist. Alina Cojocaru has danced in the lead roles of Ashtons Symphonic Variations and Michael Corder?s Masquerade. Created the roles in Vanessa Fenton?s Ad infinitum and Christopher Wheeldon?s There Where She Loves and Ashley Page?s This House Will Burn (2001).

During the 2000/2001 season Cojocaru made her debut in Anothy Dowell?s production of Swan Lake in the Pas de trois, the Neopolitan couple in Ondine, Juliet in Kenneth MacMillan?s Romeo and Juliet, Giselle in Peter Wright?s production of Giselle and Vera in Ashton?s A Month in the Country.
She was promoted to Principal after her performance of Giselle on 17 April 2001.

In the 2001/2002 season she made her debut as Kitri in Rudolf Nureyev?s production of Don Quixote, danced both Olga and Tatiana in John Cranko?s Onegin, The Sugar Plum Fairy in Peter Wright?s The Nutcracker, Nikia in Natalia Makarova?s La Bayadere and the lead role in Stephen Bayne?s Beyond Bach and Antony Tudor?s The Leaves are Fading.
In the 2002/2003 season she has made her debut in Mark Morris?s Gong and as Mary Vetsera in MacMillan?s Mayerling.
In 2003, together with Johan Kobborg, she made her debut in Giselle at the Mariinsky Theatre. Made her Bolshoi Theatre debut the same year in the ballet La Sylphide.
Took part in the Balanchine Century anniversary programme at the Mariinsky Theatre in 2004.