People do fundraising work as volunteers, as employees, and as consultants. Smaller organizations may have one volunteer or staff member who is responsible for development activities. Larger organizations may have a development office where fundraising activities are planned and managed. Specific kinds of fundraising efforts, most notably direct mail, telemarketing and capital campaigns, may also involve consultants with broad management experience or skill with specific elements of such projects. It's common for fundraising, not matter what the scale, to be supported by a group of volunteers.
In contrast to more program-specific roles in nonprofit organizations, people with a proven record of success with fundraising, or with particular elements of the work, can move from one sort of organization to another during the course of their career and, also, move back and forth between working as a consultant and being an employee. Many people find working as a fundraiser very satisfying; mobilizing the resources to do important work in the community efficiently and reliably is indeed a critical role for the success of many nonprofits, and for the field of nonprofit work more generally.
For a person seeking to have a career working for nonprofits, a common starting point is as a volunteer or entry-level worker in fundraising. Choose a cause you care about, the career counselors suggest, identify organizations that work on that cause in ways that you admire, and offer to help with their fundraising efforts. Credentials earned this way can be valuable as an entree for either program work or a career as a fundraiser. The experience will provide realistic background for whatever choices need to be made in the future.
On the Idealist.org website, a registered user can set up an alert to be notified whenever a paid or volunteer fundraising position is advertised and filter the notifications by location, field of service, and other criteria.