Solchaga was born in Tafalla in 1944. He holds a bachelor's degree in economics and business studies which he obtained from Madrid’s Complutense University in 1966. He received a master's degree from the Massachusetts Institute of Technology (MIT) in 1971.
Solchaga began his career at the Bank of Spain. He was the economic studies manager and advisor at Banco de Vizcaya from 1976 to 1979. Then he served as a minister for trade of the Basque general council of Spain from 1979 to 1980. He was the member of the Spanish Parliament from 1980 to 1995, representing Navarre Province, being part of the Socialist Party. He was one of the party officials who developed neo-liberal economic program and was among right-wing leaders of the party.
His first ministerial post was the minister for industry and energy, which he held from 1982 to 1985 in the first cabinet of Felipe Gonzalez Marquez. In a reshuffle of July 1985, Solchaga was appointed economy and finance minister to the cabinet again led by Prime Minister Gonzalez. He replaced Miguel Boyer in the post.
Solchaga resigned from office in July 1993 due to the scandal surrounded the activities of Mariano Rubio, the then governor of the Bank of Spain. The scandal is known as the Ibercorp case. Pedro Solbes replaced him as finance minister. Solchaga was named as the party's parliamentary leader in July 1993 after leaving office. However, following this period he was gradually marginalized from decision-making mechanism within the party and in 1994, he left the party.
Solchaga was also appointed chairman of the interim committee of the International Monetary Fund (IMF) in 1991. His term ended in September 1993 and the then finance minister of Belgium, Philippe Maystadt, succeeded him as chairman of the committee.