Rhianne Morris, 23, of Caterham, Surrey said: "I was on my way into work went I started having contractions so I phoned a cab.
"I was in the taxi for about ten minutes when the driver I think he was panicking a bit - said we weren't going to make it to the hospital and he was taking me to his head office and calling an ambulance.
"We arrived at the head office and then I basically had my baby in the back of the cab parked in the street outside.
"I didn't really know we weren't going to get to hospital until about 30 seconds before she arrived - up until that point I still assumed we were going to make it.
"When I realised I was going to be having her in the back of a cab my first thought was for her health and if she was going to be all right but she is absolutely fine and that was a relief."
She praised 'amazing' taxi controller Louise Hammond who helped her give birth outside the District Cars office, in Brighton Road, Coulsdon.
Louise, who was on duty at the office, rushed out and acted as an emergency midwife when it became clear that mother and baby were not going to make it to the hospital in time.
Rhianne and baby daughter Aaliyah, weighing six pounds and nine ounces, were checked by medics and delcared healthy after the rush birth.
Rhianne said: "The manager, Louise, was amazing. She was really supportive and told me when she could see the head and was very encouraging.
"I just want to thank her, really. I don't think I could have done it without her.
"She told me she would help me out with free taxis in the future. I don't know how long that will last for but she was really amazing."
Baby Aaliyah has been given the middle name Louise in recognition of the manager's help.
Louise said: "We got the call in for a woman in the early stages of labour who needed to go to hospital but that type of thing happens quite a lot.
"I sent a driver out and about ten minutes later got a panicked call from him saying that her waters had broken in the back of the cab and that the traffic in Coulsdon was really bad so he was coming back to the office.
"When she got here I was just trying to talk to her and keep her calm, asking her about contractions, that type of thing.
"We were told that the ambulance would be 45 minutes but by that time her contractions were really close together and I could tell that the baby was going to arrive much sooner than that.
"Then she started to push and I could see the baby's head, at that point it was just a case of getting the dressing gown out of her night bag and doing the best I could.
"My main concern was for the mum. She was in so much pain but she was so brave.
"After the birth the paramedics arrived and they were able to take it from there.
"It was just an amazing experience and one that I will never ever forget.
"I have been emotional all day and then the mum just sent me a picture and told me the name and that she had given her the middle name Louise. That set me off crying all over again."