Ms Johnson, 27, was shot in the head at a 30th birthday party in Peckham, south London, on Sunday May 23 and remains in hospital in a critical condition.
Five males were arrested in connection with the incident on Wednesday.
On Friday, four of the suspects were released on bail until a date in late June while Cameron Deriggs was charged with conspiracy to murder.
Deriggs, of Bromley Hill, Lewisham, appeared at Westminster Magistrates’ Court on Saturday morning dressed in a grey zip-up hoody and blue jeans.
He did not give an indication of plea.
Prosecutor Carol Udenze said: “This offence happened on May 23 at an address where a lady was shot in the head and another person was shot in the foot – this was at a house party.
“The crown’s case is that the defendant in agreement with others conspired to murder somebody at that address.”
Ms Udenze confirmed the police do not believe Ms Johnson was the intended victim.
Remanding Deriggs in custody, District Judge Michael Snow said: “This case is sent to the criminal court.
“You will be there on June 25, probably by live link, where the judge will want confirmation of your plea and give directions for the smooth running of your case.”
Several members of Deriggs’s family, including his parents, were present in the public gallery.
Ms Johnson had been among 30 guests at a silent disco in the back garden of a home in Consort Road when four men in dark clothing burst in through a side gate and shots were fired, investigators said.
Detective Chief Inspector Richard Leonard, of the Metropolitan Police, said Ms Johnson was shot in the “ensuing melee” before the suspects fled.
A second person injured only suffered a superficial wound, police said.
Ms Johnson, a mother-of-two, is a prominent member of the Black Lives Matter movement and a founding member of the Taking the Initiative party which launched last year.
She graduated with a first in social care from Oxford Brookes University, and was well known for her activism in her community.
On Monday, a vigil was held by supporters in Ruskin Park in Denmark Hill – close to the hospital where she is being treated – to pray for her to pull through.