Today’s speech comes a week after the Conservative Party won a landslide victory in a general election, and a day before Parliament begins debating legislation that would enable Britain to leave the European Union on Jan. 31 — Mr. Johnson’s central campaign promise.

Here are two issues that analysts are watching closely.

Post-Brexit timeline

There’s no doubt that Brexit will happen next month, but a key question concerns the timing of Britain’s post-Brexit transition. Mr. Johnson’s government has set a hard deadline of December 2020 for reaching a trade deal with the European Union. But Brussels, which seeks British regulations that do not diverge too far from Europe’s, is skeptical.

Ursula von der Leyen, the president of the European Commission, said on Wednesday that Mr. Johnson’s proposed timeline would be “extremely challenging,” and that Britain stands to lose more than the bloc would if the negotiations fail.

N.H.S. funding

Mr. Johnson, who has said that Britain’s revered National Health Service is his top domestic priority, is expected to promote a bill that would commit the government to spend more on it than his Conservative predecessors did. But the N.H.S. has deteriorated under the party’s watch, and some see Brexit as a further threat to its future.

In a sign of strains on the health service, 15,000 nurses went on strike in Northern Ireland on Wednesday, partly to demand that the authorities address inadequate staffing that they say endangers patient safety.