The new “two strikes” sentence will apply to any 16- and 17-year-olds who have been convicted of a second knife offence.
Adults will be handed a minimum six-month prison sentence for a second offence.
A law was passed earlier this year to allow the minimum custodial sentence to be introduced, and the government has now confirmed that the changes will come into effect from 17 July.
Campaign groups have previously warned that the new sentencing rules could result in about 200 more young people in custody.
Policing minister Mike Penning said: "We are already making sure knife offenders are properly punished, keeping more off the streets for longer and making our communities safer.
"With this new measure, we are sending out the strongest message to offenders – repeatedly take a knife onto our streets and expect to go to prison."
News that minimum term sentences will come into effect this month follows publication of Ministry of Justice figures earlier this month showing that young people convicted of a knife crime are twice as likely to receive a custodial sentence than they were seven years ago.
Statistics for the first three months of 2015 show that 13 per cent of young people convicted of a knife crime received an immediate custodial sentence, compared with just six per cent during the same period in 2008.
The MoJ says knife offences have fallen by 40 per cent between 2009 and 2014, while the proportion of those going to prison has increased by seven per cent over the same period.
