Siljander was born in Chicago, Illinois where he attended the public schools, graduating from Oak Park-River Forest High School in 1969. He received a B.S. from Western Michigan University, Kalamazoo, Michigan, in 1972 and a M.A. from the same university in 1973. He served as a trustee on Fabius Township Board in St. Joseph County, Michigan from 1972-1976 and also worked as a real estate broker. He served in the Michigan State House of Representatives from the 42nd District, 1977-1981, and was a delegate to the Republican National Convention in 1980.

Siljander was elected by special election as a Representative from Michigan's Fourth Congressional District to the Ninety-seventh Congress to fill the vacancy caused by the resignation of David A. Stockman, and was subsequently reelected to the two succeeding Congresses, serving from April 21, 1981 to January 3, 1987. He served on International Relations Middle East and Africa Subcommittees. He was an unsuccessful candidate for renomination to the One Hundredth Congress in 1986.

Siljander was appointed by U.S. President Ronald Reagan as an alternate representative to the United Nations General Assembly, serving from September 1987 to September 1988. He is president of Global Strategics, Inc., a consulting firm in Washington, D.C., operates an import-export firm and works as a radio commentator. He was an unsuccessful candidate in 1992 for nomination to the One Hundred Third Congress and is a resident of Reston, Virginia.

Siljander takes an especial interest in conflict resolution, particularly in Islamic countries, and in recent years has tried to publicise the common ground between Christianity and Islam, particularly in the Koran's portrayal of Jesus. This is a turnaround from a previous position where he objected to the Koran being read at a prayer breakfast. He is widely travelled, having visited at least four continents, and is also one of the few American politicians to have visited Libya in recent years.