Craig Dearden-Phillips, chief executive of mental health and disability charity Speaking Up, will tell the NCVO and OnBoard trustee conference in London that most trustees are not doing their jobs properly and should start acting like non-executive directors, not volunteers.
"Paying trustees would ensure that they turn up, read their papers in advance and conduct themselves in a professional way," Dearden-Phillips told Third Sector.
He said that offering trustees a small stipend of between £1,000 and £3,000 a year would lead to more diverse boards.
"The people who we most need on our boards are the ones who can't afford to do it," he said. "Trusteeship was invented at a time when the people who did it didn't need to work. If you want inclusive and broad boards of trustees, you need to include, say, single mums, young people or those without an income."
But a spokeswoman for umbrella organisation the NCVO said: "The voluntary principle is an asset that is compatible with good administration and should be retained.
"Overall, the substantial disadvantages of paying trustees outweigh the few advantages."
Dearden-Phillips said he agreed that trusteeship was part of civil society. "But you have to look at what the sector is here to do: to help the most vulnerable people in our society and to campaign on issues affecting us all," he said. "Those outcomes are best achieved through a system of governance that's more advanced than the one we've got now. The ends matter more than the means."