CONCORD, N.H. — The first openly gay Episcopal bishop and his partner of 20 years have been united in a private civil union.

The Right Reverend V. Gene Robinson was legally joined to Mark Andrew, his partner of 20 years, in a civil ceremony Saturday, the Episcopal Diocese of New Hampshire announced.

Civil unions became legal in New Hampshire this year.

The union was performed five years to the day after New Hampshire Episcopalians elected him as their bishop.

The civil and a following religious service of thanksgiving were both held at St. Paul’s Church in Concord.

Rev. Robinson had made public his intention to join his partner, but had kept the date secret out of concern about security. A spokesman, Mike Barwell, said the ceremony was intentionally private.

“Initially, the idea was to have it in a public building to make clear it was a public civil ceremony and a private thanksgiving ceremony,” Mr. Barwell said yesterday.

The plan changed out of respect for next month’s worldwide Anglican church conference in England, called the Lambeth Conference, and out of concern for the couple’s security.

Rev. Robinson had announced in March that he would have no official role in that conference, saying restrictions that organizers wanted to place on his involvement had caused him “considerable pain.”

Rev. Robinson was told last year that he could not fully participate in the once-a-decade gathering in England as the world Anglican Communion has been on the brink of schism over his 2003 election.

The civil union was performed by Ronna Wise, a longtime friend and justice of the peace.

About 120 family and close friends attended.

Rev. Robinson and Mr. Andrew decided to enter the union before Robinson’s trip to ensure they have legal protections New Hampshire’s civil union law gives gay couples. The law bestows all the rights and responsibilities of marriage, which includes inheritance and other rights enjoyed by married couples.