The Industrial and Commercial Panel re-elected him in 1992 to the 20th and in 1997 to the 21st Seanad, but he did not contest the 2002 elections to the 22nd Seanad.
Lanigan was leader of the opposition Fianna Fáil group in the 17th Seanad (1983–1987), and was Leader of the Seanad in the 18th Seanad (1987–1989). He was reappointed as Leader in the 19th Seanad (1989–1993), but resigned (along with all the Fianna Fáil whips) in May 1990 after the government lost a series of votes when no Fianna Fáil senators were present in the chamber. He later served as Chairman of the Oireachtas Joint Committee on Foreign Affairs.
Lanigan was noted as a supporter of independent Palestinian state. Lanigan founded the Friends of Palestine in the Oireachtas. In December 2003 he was awarded the Order of Bethlehem by Palestinian President Yasser Arafat. The Order, which is the highest honour bestowed on behalf of the Palestinian people, was made at a ceremony in Ramallah in which Arafat commended Lanigan for having supported the Palestinian cause "when it was not popular to do so".
Lanigan continues to be involved with the Palestinian cause, in his capacity as chairman of Irish Medical Aid for Palestine. The organisation works with all sectors of Palestinian society and with sister organisations from outside Palestine for the improvement of health in Palestine. In addition, Lanigan is a member of the Oxfam Ireland Members council.
Lanigan was an accomplished athlete. He was successful in the 100 metre hurdles at the Catholic International Student Games, before going on to win further national and international honours on the track. Lanigan was one of the founding members of the Kilkenny City Harriers athletics club in 1953.