Mas heads the “Together for Yes” alliance that won 62 seats in the 135-seat regional parliament last September.
The Popular Unity Candidacy won 10 seats and Mas needs its support to win the leadership spot and form a pro-secession parliament.
Members of the CUP voted 1,515-1,515 on the proposal for Mas to head a separatist coalition.
The Spanish government has filed a challenge against the decision to set up a road map for independence from Spain by 2017.
CUP party leaders will meet Jan. 2 to try to break the deadlock.
New elections must be called for Catalonia if no leadership deal is reached by Jan. 10., the Associated Press reported.
The region of 7.5 million inhabitants represents nearly a fifth of Spain's economic output.