Varadkar tendered his resignation as taoiseach, or premier, to President Michael Higgins after the first sitting of Ireland's lower house of parliament since an 8 February election which radically recast the political landscape.
The meeting between the two leaders will take place in the north-west of England, with Johnson still insisting the UK will leave the European Union (EU) with or without a deal on October 31
The EU is concerned that the UK wants to leave too many details about customs and regulatory checks to be agreed during the transition period after Brexit.
