Began his dance career in Slovenia. Since moving to New York, he has performed with the Martha Graham Dance Company (Principal Dancer, since 1996), Battery Dance Company, Baryshnikov's White Oak Dance Project, Robert Wilson, David Gordon's Pick Up Performance Company and MoveOpolis as well as in works of Maurice Béjart, Bula Pagarlava, Anne Bogart, Lucinda Childs, Yvonne Rainer, Susan Stroman, Steve Paxton, Larry Keigwin, Deborah Hay, Ted Shawn, Isadora Duncan and others.

His choreography was performed in both US and EU. It includes: "God is playing golf" – (winner, Benetton Dance Award), "In every one of you, One of me" (Milwaukee Dance Theater), "Where memories run free" and "K-Mart Shopper". He choreographed for students under the auspices of Battery Dance Company's Dance in Schools program. He was Assisting Choreographer to Susan McClain's "Ardent Song (Redux)", for the Martha Graham Dance Company. In 2010 he premiered "I am a Woman" during Martha Graham Dance Company's New York Season.

Tadej has taught extensively in the United States, Brazil, India, EU, Korea, China, Laos, Myanmar, Mongolia and Taiwan. He is a member of the faculty at the Martha Graham School. He established and directed Teens @ Graham (2003-06) at the Martha Graham School and was a teaching artist in New York City public schools.

In 2008 he was appointed as an Education Director of the Downtown Dance Festival and in 2010 a Manager of Special Projects for the Martha Graham Dance Company. Both positions he currently holds today. He is a founder of smARTconcierge, a consulting company for arts organizations and has established smARTfund, which awards scholarships to foreign students for their dance education in USA.

He is currently involved in a multi year teaching, choreographing and program re-shaping for the Escola de Dança de São Paulo in Brazil. In 2013, he will take a position of visiting Professor for the post diploma Curso em Pedagogia da Dança in Belem, also in Brazil. Since 2008, he is also an international teaching artist for "Dancing to Connect."

Tadej is a recipient of the 1993 Benetton Dance Award and the 2003 Eugene Loring Award. In 1993, Tadej was awarded a full scholarship at the Martha Graham School, sponsored by actor Gregory Peck. He was also a recipient of a three-year grant, given by the Ministry of Culture from Republic of Slovenia.