When the barrister William Goodhart became a Liberal Democrat life peer and frontbencher in 1997, his great aim was to reach the target set by Liberals with the Parliament Act of 1911 of a largely elected second chamber. But in September 2003 it became clear that the then prime minister, Tony Blair, would allow only the elimination of the final hereditary peers and would keep the Lords wholly appointed, with a large intake of “Tony’s cronies”. Goodhart expressed his profound feeling of “contempt and betrayal” at what he called the second chamber’s “castration”.

A skilled tactician, Goodhart, who has died gaed 83, had been successful in aligning politicians from other parties, including the Conservative leader William Hague, in pursuing an 80%-elected second chamber, as well as other reforms, mainly legal. He sought a well-equipped supreme court relatively free of politicians’ influence, an improved legal aid system and stronger bars on political corruption.

His talents were not surprising, considering the stable from which he emerged. Like his older brother Philip, the longtime Conservative MP for Beckenham, and his younger brother, Charles, the economist, William was the son of Prof Arthur Goodhart, the American-born academic lawyer who became Master of University College, Oxford, and his wife, Cecily (nee Carter). Arthur’s family descended from the German-Jewish bankers who emigrated to the US in the 19th century and established Lehman Brothers in New York.

William went to Eton, then Trinity College, Cambridge, and Harvard Law School, where he received an LLM (master of laws) qualification. Somewhat to his own surprise, he enjoyed his national service in the Oxford and Bucks Light Infantry in 1951-53, becoming a second lieutenant and remaining a member of its regimental association.

Like many young barristers, his income was quite thin after he was called to the bar at Lincoln’s Inn in 1957. “I used to go up to Cambridge to teach undergraduates law,” he said. And because he was specialising as a barrister in the Chancery division (traditionally the venue for complex civil cases), he had to struggle to stay ahead of his classes in criminal law “because I was not then – or indeed later – involved with criminal law as a practitioner”. His legal practice thrived and in 1979 he was appointed a QC. He became a bencher of Lincoln’s Inn in 1986 and was knighted in 1989.

A new political vista opened for William and his formidable wife, Celia, with the emergence of the SDP in 1981. Celia (nee Herbert), whom he had married in 1966, was political by inheritance. Her grandfather, a former deputy speaker of the House of Commons, had been raised to the peerage as Lord Hemingford on his retirement in 1943.

The Goodharts were prominent in the early SDP conferences and both emerged as candidates in the 1983 general election: William contested Kensington (the first of three attempts) while Celia stood in Kettering. In 1987 they repeated this double act, standing for the SDP Alliance. In 1992 he contested, for the Liberal Democrats, the marginal Oxford West and Abingdon seat, which was taken in 1997 by his party colleague Evan Harris. Goodhart had a favourite story about his experience in canvassing: “I rang a doorbell. A woman opened the door. I asked for her support in the forthcoming election and she answered: ‘We are not interested in party politics. We are all Conservatives here.’”

Since the Lib Dems had failed to find this vice-chairman of their policy committee a winnable Commons seat, in 1997 they named him a life peer, with a seat on the front bench in the Lords, speaking on the law and constitutional matters. He started like a just-uncorked champagne bottle, initially urging an improved system for legal aid, and quickly became the representative of the Lib Dems in the Lords on many of the upper chamber’s most influential committees.

In 1998, as a member of the committee on standards in public life, Goodhart urged the Blair government to legislate on its recommendations. When it did so, with the Political Parties, Elections and Referendums Act of 2000, he strongly welcomed it. This set up the Electoral Commission, compelled the disclosure of donors, limited such donations to those on electoral lists and set limits on campaign spending.

What then absorbed Goodhart’s ever-renewed energy, above all, was his campaign to democratise the second chamber so that two-thirds or four-fifths of its members would be elected for 15-year terms, and the rest chosen from among “the great and the good”. With the House of Lord Act 1999 that removed all but 92 of the hereditary peers, Goodhart paid tribute to the past contributions of the hereditaries, but said that their disappearance was 88 years overdue.

He retired from the Lords in 2015.

He is survived by Celia, their son, Benjamin, two daughters, Laura and Frances, eight grandchildren and Charles.

• William Howard Goodhart, Lord Goodhart, lawyer and politician, born 18 January 1933; died 10 January 2017

• Andrew Roth died in 2010