[3] Allen was a general practitioner who represented a wide range of clients from a Black Muslim prisoner[4] to depositors in a failed country bank.

His legal interests were broad, and as a result over his long career he handled cases involving a variety of issues including witchcraft, alienation of affection, obscenity, as well as election disputes and contested utility rates.

It was during this period that he undertook a civil rights case representing Fred Wallace, an African American law student at Harvard University who had been charged in Prince Edward County, Virginia, where he had been doing civil rights work, with multiple misdemeanors and a felony.

In recognition of his work in the Wallace case, The American College of Trial Lawyers gave Allen its first Award for Courageous Advocacy.

In 1971, Allen undertook the appeal of a North Carolina homeowner who had brought a Federal Tort Claims Act action against the United States for property damage to his house allegedly caused by the sonic boom of military aircraft carrying out a training mission over North Carolina.