Kevin Wilson, 22, kicked and stamped on Malorie Bantala's stomach when she was eight months pregnant with his son after she refused to have an abortion.
He was found guilty of child destruction and GBH on 17 December.
Wilson will serve at least 16 years in prison. His accomplice, Taffari Grant, 17, was given a 10-year custodial sentence, plus four years on licence.
Miss Batala, 22, suffered life-threatening injuries when she was attacked in Peckham on 15 June 2015.
The Old Bailey had heard how Wilson, a teaching assistant, recruited Grant to help him attack Miss Bantala.
On the day of the assault, she had been buying decorations for her baby shower, returning home at about 20:00 BST.
As she approached her flat, Wilson and Grant emerged from some bushes where they had lain in wait disguised in crash helmets.
They launched a vicious attack, kicking and stamping on Miss Bantala's stomach as she lay curled up on the ground, trying to protect her unborn child with one hand.
The pair fled on a scooter. Family and neighbours ran to her aid, but her baby was stillborn later in hospital.
Miss Bantala lost six pints of blood and was also left with two broken fingers in the hand she had used to try to shield her baby, whom she had named Joel.
"The moment Joel died inside me I lost everything, literally. Life as I knew it no longer made sense," she said in a statement.
A man who killed his ex-girlfriend's unborn child during an attack in south-east London has been jailed for life.