He attended Phillips Andover Academy and graduated from Harvard College in 1864, and from Harvard Law School in 1866. He was admitted to the bar and commenced practice in the firm of Evarts, Southmayd & Choate in New York City. In 1869, he formed a partnership with Ex-Secretary of State of New York Francis C. Barlow. In 1872, Barlow took office as State Attorney General and Olney helped with the prosecution of the members of the Tweed Ring.
He married Mary Sigourney Butler, and they had four sons: Peter B. Olney, Jr. (1881-1968), Richard Olney, Wilson Olney and Sigourney B. Olney.
In 1875, Olney ran on the Tammany ticket for New York County District Attorney but was defeated by the incumbent Republican Benjamin K. Phelps. Afterwards Olney left Tammany and joined the "County Democracy", the Anti-Tammany Democrats of New York City. After the death of D.A. John McKeon and the resignation of Wheeler H. Peckham after only a week in office, Governor Grover Cleveland appointed Olney in December 1883 as D.A. to fill the vacancy until the end of 1884.
From 1897 until his death, he practiced law as senior partner of the firm of Olney & Comstock. From 1898 on he was also a U.S. Referee in Bankruptcy. In 1919, he was appointed by Surrogate Fowler as referee to investigate claims against the estate of the deceased actress Anna Held.
- LOCAL POLITICAL NOTES in NYT on October 23, 1875
- WHEELER H. PECKHAM RESIGNS.; ILL HEALTH CAUSES HIM TO GIVE PLACE TO PETER B. OLNEY AS DISTRICT ATTORNEY in NYT on December 10, 1883
- THE NEW DISTRICT ATTORNEY in NYT on December 12, 1883
- PETER BUTLER OLNEY DIES OF PNEUMONIA in NYT on February 10, 1922
Wheeler H. Peckham
| New York County District Attorney
1883 - 1884
Randolph B. Martine