First United Church, Church building in Centretown Heritage Conservation District, Ottawa, Canada

First United Church is a United Church of Canada congregation in Ottawa that formed in 1846. Its first permanent home was built in 1862 at Elgin and Albert Street, and the current building in Centretown was constructed in 1911. In 2007 the congregation sold that structure and moved to Westboro, sharing a building with All Saints Westboro.

First United formed in 1846 as a Congregationalist congregation, one of Ottawa's oldest. Its first permanent home was built in 1862 at Elgin and Albert Street, and the Centretown building dates from 1911. In February 1925 it merged with the former Westminster Presbyterian Church, which had voted for Union, becoming First United Church of Ottawa four months before the United Church of Canada was officially formed.

The congregation's name and identity come from its 1925 union with Westminster Presbyterian, four months before the United Church of Canada was formally constituted. Since Rev. Sharon Moon's 1987–2004 tenure it has been known for welcoming gay people, fighting poverty and supporting people with addictions, and it is an Affirming Congregation of Affirm United.

The congregation left its Centretown building in 2007 and now shares the All Saints Westboro building, with separate services for the United and Anglican congregations. Visitors heading to the former Elgin and Albert site will find no First United service there; check the Westboro location before planning a visit.

In February 1925, four months before the official union, the congregation merged with the former Westminster Presbyterian Church, a post-1900 split from Erskine Presbyterian Church, to become The First United Church of Ottawa. The congregation sold its historic building in 2007 and moved to Westboro, sharing a building with All Saints Westboro, an Anglican congregation, while holding separate services.