"main role was" is grammatically correct and can be used in written English.
It is typically used to describe the most important or significant responsibility or function that someone or something has. Example: In the play, her main role was that of the protagonist, representing the struggle against injustice and oppression.
Its main role was in helping determine where and how far spores had spread.
His main role was to organise and sustain radio communications in difficult conditions.
As FRG leader, Nelson's main role was to act as communications liaison between the Army and the company's families.
Sappington's main role was data analysis, striving to determine which genes were amplified in response to disease.
Throughout the history of Greek art, the architect's main role was to design cult buildings, and until the Classical period it was virtually his only concern.
"Natalia's main role was coordinating, including regular coordination with Chaika, whom she knew personally," said a source acquainted with the Prevezon case.
The main role was played by subjective factors connected to very specific people — Gorbachev and his advisers Yakovlev and Shevardnadze — and their supporters".
He was consulted by Sir Winston Churchill and other Allied leaders, but his main role was to prevent Germany and Italy from conquering North Africa.
They thought that the best bosses pretty much left their people alone, and that their main role was to help with technical problems when people got stuck.
It is produced by cells, and for years scientists thought that its main role was to hold them in their proper position.
Its main role was to undermine the official Dutch Communist party, the KPN, by denouncing its deviant beliefs and unreliable conduct, and to garner information on - and gain access to - the Maoist elite in Beijing.
