1921 | Born in Hamilton, Ontario. |
| 1942 | Receives Bachelor of Arts degree from University of Toronto. |
| 1942-1946 | Serves overseas in Second World War, R.C.A.S.C., Lieutenant. |
| 1949 | Becomes Barrister at Law (with Honours), Osgoode Hall Law School, Toronto. |
| 1949-1952 | Assistant Director, Canadian Survey of the Legal Profession. |
| 1952-1955 | Practices law with Edmonds, Maloney, Nelligan and Edmonds, Toronto. |
| 1954-1957 | Secretary, Ontario Section, Canadian Bar Association. |
| 1955 | Moves to Ottawa. |
| 1955-1963 | Practices law with McIlraith & McIlraith, Ottawa. |
| 1957-1960 | Chairman, Legal Aid Liaison Committee, Canadian Bar Association. |
| 1960-1962 | Acts as legal advisor for Eastview (now Vanier); a key player in Eastview's achievement of city status on January 1, 1961. |
| 1963 | Opens his own law firm - John P. Nelligan, Barrister at Law. |
| 1965-1967 | Chairman, Civil Liberties Section, Canadian Bar Association. |
| 1965-1969 | Director, The Advocates' Society. |
1969 1972
| Establishes partnership with Denis Power to create the law firm Nelligan Power LLP (now Nelligan O'Brien Payne LLP). Queen's Counsel. |
| 1972-1974 | President, Canadian Civil Liberties Association. |
| 1974-1977 | Member, National Executive, Canadian Bar Association. |
| 1975-1983 | Dredging case-Acts as lawyer for Sceptre Dredging, on of 21 leading dredging companies charged by Crown with conspiracy to defraud the government. Charges against Sceptre were dropped. |
| 1976 | Fellow, American College of Trial Lawyers. |
| 1979-1981 | Chairman, Legislation and Law Reform Committee, Canadian Bar Association. |
| 1980-1985 | Director, The Advocates' Society. |
| 1981-1983 | Vice President, The Advocates' Society. |
| 1983-1984 | President, The Advocates' Society. |
| 1982-1984 | Councillor, Medical-Legal Society of Ottawa-Carleton. |
| 1986 | Fellow, International Academy of Trial Lawyers. |
| 1987 | Obtained a key win against Ontario Hydro and Atomic Energy of Canada, Ltd. - $1.4 million awarded in damages, interest and cost. Mr. Nelligan also negotiated an out of court settlement with AECL on behalf of his client. |
| 1988-1991 | President, The Thomas More Lawyers' Guild of Ottawa. |
| 1988-1999 | Certified by Law Society of Upper Canada as a Specialist in Civil Litigation and Criminal Law. |
| 1990 | Lawyer for a former Liberal cabinet minister against federal government charges of fraud and conspiracy; charges are eventually dismissed. |
| | Lawyer for a Liberal Senator against government charges of misuse of Senate supplies and services; charges are eventually dropped. |
| 1991 | Receives honorary Bachelor of Law degree from Osgood Hall (York University). |
| | Receives the Law Society of Upper Canada Medal. |
| 1992-1996 | Chairman, Court Reform Implementation Task Force, Canadian Bar Association. |
| 1993-1995 | Director, American College of Trial Lawyers, Province Committee. |
| 1993-1998 | Member, American College of Trial Lawyers, Attorney-Client Relationship Committee. |
| 1994 | Receives the Laidlaw Medal for Excellence in Advocacy. |
| | Lawyer in suit against Red Cross for wrongful dismissal; wins case, Client awarded over $200K in damages and has name cleared in media. |
| 1995 | Receives the Advocates' Society Medal. |
| | Acts as Committee Counsel for Senate Inquiry into privatization of Toronto's Pearson Airport. |
| 1998 | Receives Award of Merit from B'nai Brith Canada. |
| 2000 | Life Member, The Law Society of Upper Canada. |
| | 50 Years at the Bar, County of Carleton Law Association. |
2001 2009 | Receives Medal of Honour from County of Carleton Law Association. Celebrates his 60th Anniversary of Call to the Ontario Bar. |