Earlier at the conference Lib Dem members voted overwhelmingly to back her proposal for a manifesto pledge to revoke Article 50 if the party came into power with a majority government.
She told the BBC's Andrew Marr Show: "If the Liberal Democrats win a majority at the next election, if people put [us] into government, as a majority government, the "stop Brexit" party, then stopping Brexit is exactly what people will get".
He is the sixth MP to defect to the Lib Dems this year, following former Change UK MPs Chuka Umunna, Luciana Berger and Angela Smith and former Tory MP Phillip Lee, and brings their number of parliamentarians to 18.
Former universities minister Sam Gyimah was announced as a new member of the Liberal Democrats at its annual conference in Bournemouth, on the southern English coast.
She will say Mr Johnson is "silencing critics, purging opponents, ignoring the law".
"The truth is you can't plan for no deal".
A no-deal Brexit would be like "burning your house down", Ms Swinson will add. "You might have insurance, but you're still going to lose all your stuff".
"Despite calling herself a democrat, Jo Swinson's mask has slipped and we now know that she wants to overrule one of the largest democratic votes in British history, cancelling Brexit", the Braintree MP said.
"Brexit will put lives at risk".
He said most voters now know "in no uncertain terms" that a vote for the Lib Dems is to "unequivocally" stop Brexit.
"Even now, when faced with all the clear and obvious dangers that Brexit brings, Jeremy Corbyn still insists that if Labour win a general election, they will negotiate their own Brexit deal to take us out of the European Union", she will say.
Asked whether the party would stand aside for Labour candidates, the Lib Dem leader said: "That's a different question because Labour are not a remain party, Labour are trying to deliver a Labour Brexit". "Our country needs us at this precarious time".
"In the discussions that are happening about remain parties working together - that's remain parties where there might be some electoral alliances - that's parties that actually want to remain and of course that doesn't include the Labour party, but in most places the biggest and strongest party of remain will be the Liberal Democrats".
At the suggestion the party had morphed into the anti-Brexit Party - as opposed to Nigel Farage's Brexit Party - she said: "We are not a single issue party, we are a party with more than a century of liberal heritage".