The 60-year-old was reportedly killed with wife Heather after the helicopter came down in a mountainous area of New Mexico.
Mr Bennett spent years campaigning against Mugabe and was famously jailed in 2009 while trying to negotiate a power-sharing government with the dictator.
Following his release and fearing further charges against him he fled to South Africa.
Former Zimbabwe government minister David Coltart wrote on Facebook, “I have just confirmed from three separate reliable sources that Roy and Heather Bennett have been tragically killed in a helicopter accident in North America.
Bennett lived in South Africa on political asylum, which was first granted in 2007, and fled again after he was jailed on his return.
The politician was former treasurer general of the Movement for Democratic Change Tsvangirai (MDC - T) which is currently Zimbabwe's main opposition party.
MDC-T vice-president Nelson Chamisa has alsom mourned his death.
Police in New Mexico confirmed the crash and says it occured in a rural area of the state.