Adults without an A-level or equivalent qualification will be offered a free college course, the government has announced.
The offer will be available from April for people in England and applies to courses offering "skills valued by employers," according to Downing Street.
Boris Johnson will use a speech on Tuesday to outline his intention to create conditions for people to upskill at any stage of their life, amid fears of a sharp spike in unemployment.
His pledge comes after Chancellor Rishi Sunak last week, when unveiling his plan to support jobs after the furlough scheme is wound down next month, admitted not every job can be saved following the hit that Covid-19 has dealt the economy.
The Prime Minister is planning to say: "As the Chancellor has said, we cannot, alas, save every job.
"What we can do is give people the skills to find and create new and better jobs.
"So my message today is that at every stage of your life, this Government will help you get the skills you need."
The guarantee, according to Downing Street, will see adults without an A-level or equivalent qualification offered a free, fully funded college course to provide them with "skills valued by employers".
They will also be given the opportunity to study at a time and location that suits them.
This offer will be available from April in England, and will be paid for through the National Skills Fund - which will be topped up with an additional £2.5 billion.
A full list of available courses will be announced next month, Number 10 confirmed.
The Prime Minister is expected to add: "We're transforming the foundations of the skills system so that everyone has the chance to train and retrain."
As part of the measures, the Government plans to make higher education loans more flexible, allowing adults and young people to space out their study across their lifetimes, rather than undertake it all in three to four-year intensive blocks.
Ministers believe the shake-up will allow would-be students to take more high-quality vocational courses in further education colleges and universities, while allowing people to retrain for the "jobs of the future".
These reforms will be backed by continued investment in college buildings and facilities, with more than £1.5 billion earmarked for capital funding, No 10 said.
Apprenticeship opportunities will also be increased as part of the Prime Minister's plan, with more funding for small and medium-sized enterprises taking on apprentices, and greater flexibility in how their training is structured, especially in sectors such as construction and creative industries, the Government is set to announce.
The CBI called the Government's learning reforms a "strong start".
Director general Dame Carolyn Fairbairn said: "Retraining was already a vital priority for the UK.
"The significant unemployment coronavirus is leaving in its wake only accelerates the need for people to develop new skills and adapt to new ways of working.
"The lifetime skills guarantee and flexible loans to support bitesize learning are a strong start. But to really shift gears, this must be backed up by meaningful progress on evolving the apprenticeship levy into a flexible skills levy."