Caspar Bowden, who has died of cancer aged 53, warned of online state snooping many years before Edward Snowden, and ran a successful campaign to stop surveillance laws becoming even worse than they are. He entered the fray in 1997, when Tony Blair went back on a pre-election promise not to demand government access to cryptographic keys. At a Scrambling for Safety conference convened at the London School of Economics to thrash out a response, Caspar emerged as knowledgable, articulate and passionate.

He was born in London, the only child of Kenneth and Angela Bowden, though he had two older half-brothers, Malcolm and Simon. He attended Westminster school and read mathematics at Magdalene College, Cambridge, but spent a lot of time working on artificial intelligence and failed his degree. He found a job as a programmer at Island Logic, then moved to Goldman Sachs, working on projects including option pricing and cryptographic software. He became an active member of the Labour party in Islington, and by 1997 was chair of Scientists for Labour.

The “Crypto War” had started in 1993 when the US National Security Agency persuaded the new Clinton administration to try to bully US firms into encrypting data using the Clipper chip, a device containing a back-door key to let the NSA decipher any encrypted phone call or email just as easily as the intended recipient. Industry fought back, and throughout the 1990s there were repeated tussles, with US officials claiming that unregulated crypto would make police wiretaps “go dark”, while technologists countered that giving spare keys to governments would make systems more complex and fragile, and businesses feared that regulation would kill the dotcom boom. Before the election, New Labour had promised that they would not introduce a power to demand crypto keys. But suddenly the Crypto War had come to Britain too.

Caspar saw this U-turn as a betrayal, resigned from the Labour party, and set up the Foundation for Information Policy Research, of which he became director. He threw himself into the fight against the Regulation of Investigatory Powers bill and secured several major changes. The most important was the “big browser” amendment, which defined the boundary between “content” and “traffic data”.

Previously, a police officer needed a warrant signed by a secretary of state to wiretap a phone (getting the “content” of the call) but could get phone bill records of who called whom when (the “traffic data”) with a simple order. The police wanted “traffic data” to mean a whole URL, but Caspar explained patiently that a web search for “pregnancy tests”, for instance, resulted in a URL that contained those actual search terms, and would thus give the police information that most reasonable people would consider to be “content”. He got his amendment.

Caspar’s second big achievement as director of FIPR was to get NGOs to Brussels. By 2002 it was becoming clear that many digital rights issues would be fought in Brussels; export controls on software were the issue of the day. He saw that human-rights and digital-rights NGOs needed a presence there, and started the process that led to the birth of the advocacy group European Digital Rights (EDRi).

In 2002, Caspar left FIPR and joined Microsoft, where he became chief privacy adviser for Europe, the Middle East and Africa. Microsoft was originally keen on privacy, and Caspar got the company to sponsor privacy research in various ways. But the company’s direction changed as cloud services became important and as the Bush surveillance laws gave the agencies access to cloud data. In 2011 Caspar left. As he told the story, he was responsible for briefing Microsoft’s government sales managers in 40 countries about privacy, and told them that if they sold Microsoft cloud services to non-US governments, the US Fisa court (the Foreign Intelligence Surveilliance court) would give the FBI, NSA and CIA unfettered access to everything. For this, he was fired.

After 2011 he went back to being a privacy campaigner, as a member of Liberty’s policy council and a board member of the Tor project, whose software lets people browse the internet anonymously. He was the first to explain how much cloud services expand state surveillance, and that the EU was wilfully blind to the NSA’s activities.

Some saw this view as extremist, but the Snowden revelations of 2013 vindicated him completely. Some months afterwards, he wrote a powerful paper for the European parliament’s committee on civil liberties, justice and home affairs, LIBE, setting out in detail how US law, policy and technology fit together to undermine human rights and the rule of law in other countries.

Caspar was not only passionate about privacy, but was an effective public speaker and a charming man in private. He had a knack for explaining complex technical issues in language that even members of the House of Lords could understand. While he was a fan of technology, he was sufficiently clear-sighted to understand the hazards as well as the opportunities. Now that we seem headed for a second Crypto War, with both the prime minister, David Cameron, and the FBI director, James Comey, gearing up to demand government access to all our keys and data, we shall sorely miss him.

He is survived by his wife Sandi (nee Cox), whom he married in 2005. It is proposed to establish the Caspar Bowden Foundation to promote privacy as a universal human right.

• Caspar Pemberton Scott Bowden, privacy campaigner, born 19 August 1961; died 9 July 2015