His speeches were so impassioned that both he and the congregation feared reprisals from Southern sympathizers, so several members of the church quietly armed themselves and watched over the pulpit on Sundays.

His attacks on the Fugitive Slave Law drew discussion in one of President Buchanan's cabinet meetings of indicting the minister for treason.

Desiring a larger and more elegant edifice to reflect the growth of the congregation, church members voted to construct a second building.

The sanctuary features a hammer-beam ceiling, painted rust red and stenciled with gold-leaf daffodils, which is complemented by blue walls.

Frances Ellen Watkins Harper, the first woman of African descent to have her writings published in the United States, was a member of First Church from 1870 until her death in 1911.

[3] The day after John Brown was executed, his body came to Philadelphia for a private vigil attended by William Henry Furness, then was taken to North Elba, New York, and buried.

[4] In July 2010, executives from Monsanto visited the church to discuss the adoption of a code of ethics for the field of biotechnology, a sort of Hippocratic oath, akin to a doctor's pledge to "do no harm".

[5][6] In February 2016, as part of a nationwide effort among UU congregations, the congregation unanimously adopted the following statement of support for the Black Lives Matter movement: In line with our commitment to affirming the inherent worth and dignity of all people, we, the First Unitarian Church of Philadelphia, declare that black lives matter.

We support the Black Lives Matter movement and pledge our congregation's dedication to participating in anti-racist, anti-oppression work within our own community; to acknowledging our denomination's and our congregation's checkered racial history; and to serving as allies, witnesses, and partners in our country's continued struggle for racial justice and equity.A corresponding banner was installed on the church porch, facing Chestnut Street.

First Unitarian is a regional community center that provides meeting space on a non-discriminatory basis for many different groups and activities: yoga and aerobics classes, meditation, Narcotics Anonymous meetings, forums by the Americans for Democratic Action and Common Cause, Black Women's Art Festival, Islamic Relief Day of Dignity, Philadelphia Fringe Festival events, and citywide vigils honoring victims of violence in Philadelphia.

In November 2007, Rolling Stone magazine featured the church as one of the top alternative rock venues thanks to the success of the events organized by R5 Productions in the basement, chapel, and sanctuary.

First Unitarian also draws parents of young children and youth with religious education programs that promote value-based learning about one's responsibility to one another and to the Earth.