United Kingdom investigators also questioned whether Facebook failed to maintain adequate safeguards to ensure other third-party app developers had not misused social data.
The fine "sends a clear signal that I consider this a significant issue, especially when you look at the scale and the impact of this kind of data breach", said Information Commissioner Elizabeth Denham.
The report sets out regulatory action taken against a number of the star players in this year's data scandal, including a criminal prosecution against Cambridge Analytica's parent biz SCL Elections Ltd - which has since folded, in name at least - for failing to properly deal with the ICO's enforcement notice.
Despite the proposed fine being a record for the watchdog, campaigners said it was "unacceptable", as under new data laws the penalty could have totalled more than £450 million. If the incidents had occurred more recently - such as after the new European General Data Protection Regulation (GDPR) had taken effect - the company could have faced fines of £17 million, or even £1.4 billion (around 4% of its global turnover).
The Commons' Digital, Culture, Media and Sport Committee said Ms Denham's inquiry has found that Facebook "contravened the law by failing to safeguard people's information". The ICO wants parties to undergo compulsory audits of their use of personal data, including the purchase of marketing lists and lifestyle information to help target voters. "But this can not be at the expense of transparency, fairness and compliance with the law", she said in a statement.
"We are fully cooperating with the investigation now under way by the Australian Privacy Commissioner and will review any additional evidence that is made available when the UK Office of the Information Commissioner releases their report", the spokeswoman said. "Trust and confidence in the integrity of our democratic processes risk being disrupted because the average voter has little idea of what is going on behind the scenes". "We have been working closely with the ICO in their investigation of Cambridge Analytica, just as we have with authorities in the U.S. and other countries".
Facebook has said it will be reviewing the report and responding to the ICO soon.
Cambridge Analytica has maintained that none of the data obtained without the knowledge of Facebook users was shared with or used for the purposes of the Trump campaign during the 2016 election.
ICO, which does not normally publish its findings, said it would give the public another update on its investigation in October.
"The number of Facebook users affected by this kind of data scraping may be far greater than has now been acknowledged".