Johnson hopes to win a majority to push through the last-minute Brexit deal he struck with the EU last month, while opposition Labour leader Jeremy Corbyn has promised to renegotiate the exit agreement and then hold another referendum.
Setting out their post-Brexit immigration policy, the Conservatives said they would treat EU and non-EU migrants the same from January 2021, including a five-year wait to obtain welfare payments and a surcharge to access health services.
"As we come out of the EU we have a new opportunity for fairness and to make sure all those who come here are treated the same. We will make our immigration system equal," Johnson said in a statement.
The Conservatives lead Labour by 10-17 percentage points, four polls late on Saturday showed.
Both parties are expected to publish their election manifestos this week, setting out in detail their full set of policies for government. Corbyn and Johnson are due to go head-to-head in their first televised debate on Tuesday evening.
Johnson failed to get his deal approved by parliament ahead of a Oct. 31 Brexit deadline in part due to a rebellion by some of his own lawmakers over the speed at which he proposed to push through the legislation.