Fensterwald graduated from Harvard Law School in 1949. He entered the Georgetown University School of Advanced International Studies, a private institution, and received an M.A. in 1950. From 1951 to 1956 Fensterwald worked for the State Department as an Assistant Legal Advisor. This included defending State Department employees accused by Joseph McCarthy of being members of the American Communist Party.
In 1957 Fensterwald was hired by Thomas C. Hennings as an investigator for the Senate Committee on Constitutional Rights. Later that year Fensterwald visited the Soviet Union. According to Alan Weberman on his return the FBI stated, "Fensterwald has gone out of his way to be helpful."
Fensterwald also worked as a foreign policy advisor to Estes Kefauver. On March 12, 1961, Fensterwald became an investigator for the Senate Antitrust and Monopoly Subcommittee that was headed by Kefauver. However the two men fell out and later that year Kefauver sacked Fensterwald.
Edward V. Long selected Fensterwald as his Chief Counsel when he had been accused of being corruptly involved with Jimmy Hoffa. The two men lived in the same apartment building in Washington. Long was also connected to Robert Maheu and Sam Giancana.
In 1967 Long was called before the Senate Ethics Committee and questioned about his connections to Hoffa. As a result of this investigation Long was forced to resign in December 1968. Long's book, The Intruders, was dedicated to Fensterwald.
Fensterwald became involved with Jim Garrison and his investigation of the John F. Kennedy assassination. In January 1969, Fensterwald joined forces with Richard E. Sprague to form the Committee To Investigate Assassinations, which was mainly concerned with finding the people responsible for killing Kennedy. As a result of the investigation Fensterwald and Michael Ewing co-authored Assassination of JFK: Coincidence or Conspiracy.
In 1974 Richard Case Nagell employed Fensterwald as his lawyer. In September, 1963, Nagell had walked into a bank in El Paso, Texas, and fired two shots into the ceiling and then waited to be arrested. Nagell claimed he did this to isolate himself from the assassination plot. This was successful and Nagell was charged with armed robbery and ended up spending the next five years in prison.
On his release Nagell told Jim Garrison about his knowledge of the assassination of John F. Kennedy . He claimed that David Ferrie, Guy Banister, and Clay Shaw were involved in this plot with Lee Harvey Oswald. However, Garrison decided against using him as a witness in the court-case against Shaw.
Fensterwald employed Lou Russell as a private detective to help him with some of his legal cases. One of Russell's first tasks was to investigate the journalist Jack Anderson. Russell also purchased $3,000 in electronic eavesdropping equipment from John Leon of Allied Investigators. Russell's friend, Charles F. Knight, was told that this equipment had been purchased for James W. McCord. At the time, Russell also did part-time work for McCord. This equipment was used to tape the telephone conversations between politicians based at the Democratic Party National Committee and a small group of prostitutes run by Phillip Mackin Bailley that worked their trade in the Columbia Plaza.
On 16th June, 1972, Lou Russell spent time at his daughter's house in Benedict, Maryland. That evening Russell traveled to Washington and spent between 8.30 until 10.30 p.m. in the Howard Johnson's Motel. This was the motel where those involved in the Watergate burglary were staying. However, Russell later told FBI agents that he did not meet his employer, James W. McCord, at the motel. Russell then said he drove back to his daughters in Maryland.
Soon after midnight Russell told his daughter he had to return to Washington to do "some work for McCord" that night. It was estimated that he arrived back at the Howard Johnson's Motel at around 12.45 a.m. At 1.30 a.m. Russell had a meeting with McCord. It is not clear what role Russell played in the Watergate break-in. Jim Hougan has suggested that he was helping McCord to "sabotage the break-in".
Later that night Frank Sturgis, Virgilio Gonzalez, Eugenio Martinez, Bernard L. Barker and James W. McCord were arrested while in the Democratic Party headquarters in Watergate. McCord employed Fensterwald as his lawyer.
On 21st December, 1972, James W. McCord wrote a letter to Jack Caulfield: " Sorry to have to write you this letter but felt you had to know. if Helms goes, and if the WG (Watergate) operation is laid at the CIA's feet, where it does not belong, every tree in the forest will fall. It will be a scorched desert. The whole matter is at the precipice right now. Just pass the message that if they want it to blow, they are on exactly the right course. I'm sorry that you will get hurt in the fallout.”
Caulfield was unable to persuade Richard Nixon to leave the CIA alone. On 30th January, 1973, McCord, Gordon Liddy, Frank Sturgis, E. Howard Hunt, Virgilio Gonzalez, Eugenio Martinez, and Bernard L. Barker were convicted of conspiracy, burglary and wiretapping.
In February, 1973, Richard Helms was sacked by Nixon. The following month James W. McCord carried out his threat. On 19th March, 1973, McCord wrote a letter to Judge John J. Sirica claiming that the defendants had pleaded guilty under pressure (from John Dean and John N. Mitchell) and that perjury had been committed.
James W. McCord also gave more details about Operation Gemstone. In a statement given to Sam Ervin on 20th May he claimed that there was a plot to steal certain documents from the safe of Hank Greenspun, the editor of the Las Vegas Sun. According to McCord, the plot was organized by John N. Mitchell, Gordon Liddy and E. Howard Hunt were to carry out the break-in and that people connected to Howard Hughes were to supply them with a getaway plane.
In 1974 McCord published a book on his involvement in Watergate, A Piece of Tape - The Watergate Story: Fact and Fiction. McCord claimed that Dorothy Hunt told him that her husband, E. Howard Hunt, had "information which would impeach the President (Nixon)". McCord also wrote: "The Watergate operation was not a CIA operation. The Cubans may have been misled by others into believing that it was a CIA operation. I know for a fact that it was not."
In April 1973, Lou Russell suffered a heart attack. However, despite being unable to work, James W. McCord continued to pay him as an employee of Security International. Russell did not have a bank account and Fensterwald paid his cheques into his Committee to Investigate Assassinations.
Another of Fensterwald's famous client was James Earl Ray, the man who had been found guilty of killing Martin Luther King. In June 1974 Fensterwald filed a motion to grant Ray a new trial on the basis of alleged collusion between his former attorney and the author William Bradford Huie. In 1976 Ray dismissed Fensterwald as his lawyer. Fensterwald also represented Andrew St. George.
On 24th September, 1978, John Paisley, the former CIA official, took a trip on his motorized sailboat on Chesapeake Bay. Two days later his boat was found moored in Solomons, Maryland. Paisley's body was found in Maryland's Patuxent River. The body was fixed to diving weights. He had been shot in the head. Police investigators described it as "an execution-type murder". However, officially Paisley's death was recorded as a suicide. In June 1979 Fensterwald represented Paisley's family but was unable to solve the case.
According to Robert D. Morrow, Fensterwald in February, 1991 arranged "to interview an Air Force colonel... who I had identified as the possible bagman (responsible for paying the conspirators) for the JFK assassination". Morrow told Gus Russo that "Bud is going to get himself killed" if he went ahead with this interview.
On April 2, 1991, Bernard Fensterwald, 69, died of a heart attack at his home in Alexandria, Virginia. Robert D. Morrow is convinced he was murdered but his wife insists he died of natural causes.