On academic scholarship, Neil attended Fordham College from which he graduated in 1964 with a BS degree in Political Science. While in law school at the University of Toledo, he was named the editor-in-chief of the Law Review and was also selected as outstanding student in his class. Upon graduation from law school, Neil became an associate in the firm of Garry Cahill & Edmunds and two years later became a partner in a new firm entitled Garry, Cahill, Edmunds & Breslin. In 1981, Neil formed a partnership with his two brothers, Michael (currently Albany County Executive) and Thomas (currently Albany County Court Judge). Currently, Neil practices law as "of counsel" to the firm of Hiscock & Barclay.

Neil has been a community leader for many years. His involvement in civic and social areas in Albany includes 15 years as a board member of Arbor House, a residence facility for women in need. He also served as president of Arbor House for a period of seven years. Neil has been the attorney for St. Anne's Institute in Albany and has done work for Hospitality House, the International Center and Hope House, a drug treatment facility. Further, Neil was Vice President of the Interfaith Partnership for the Homeless from 1994 to 1998.

An active member of the New York State Bar Association, Neil has served as a lecturer on real estate law; editor of the newsletter of the New York State Bar Association General Practice of Law Section from 1980-1984; member of the Executive Committee of the General Practice of Law Section from 1980-1985 and from 1989-1998; chairperson of the General Practice of Law Section from 1993-1994; and member of the House of Delegates of the New York State Bar Association from 1992-1994. Additionally, he has been a member of the Character and Fitness Committee of the Appellate Division, Third Department since 1987 and was chairman of the Grievance Committee for the Albany County Bar Association from 1985-1993.

Neil serves as a member of the Executive Committee and is the former Chair of the State/Federal Relations Committee of the National Conference of Insurance Legislators (NCOIL). In recognition of his dedication and commitment, Senator Breslin has received awards from numerous organizations including Capital Area Council of Churches, the Legal Project, the Homeless Action Committee, Upper Hudson Planned Parenthood, Caregivers Respite Services of Catholic Charities, University at Albany's Presidential Honors Society, New York State Bar Association, American Civil Liberties Union, KidsPeace National Centers, Nelson A. Rockefeller College of Public Affairs and Policy ("Distinguished Public Service Award") and Robert F. Kennedy Democratic Club ("Profiles in Courage Award"). In addition, in 2009, he was the recipient of the Pathways of Hope Award given by the Clearview Center, the Advocacy Award given by the International Center of the Capital Region, the Community Service Award from Centro Civico Hispanoamericano; and was honored by the Capital District Area Labor Federation for years of service to the labor movement and working families.