The daughter of a vicar made her speech shortly before the deadline for nominations closed on Thursday.
Ms May said: "I know some politicians seek high office because they are driven by ideological fervour. I know others seek it for reasons of ambition or glory.
"My reasons are much simpler.
"I grew up the daughter of a local vicar and the granddaughter of a regimental sergeant major. Public service has been a part of who I am for as long as I can remember.
"I know I'm not a showy politician, I don't tour the TV studios, I don't gossip about people over lunch, I don't go drinking in Parliament's bars.
"I don't often wear my heart on my sleeve.
"I just get on with the job in front of me."
Theresa May leads Boris Johnson among Tory party members (1/3) https://t.co/LqZ5Qm4Tuf pic.twitter.com/WQwAbPcLfp
— YouGov (@YouGov) June 29, 2016
Speaking in 2012, she said: "I am a practising member of the Church of England."
She was a quiet supporter of Remain during the referendum in June and she has clarified that she will prevent Brexit.
Pro-Brexit MP Boris Johnson has ruled himself out of race to be the next Tory leader.
Fellow Leave campaigner and Justice Secretary Michael Gove has announced he will run.
He will also be up against Christian and work and pensions secretary, Stephen Crabb.
Liam Fox, former Secretary of State for Defence, will also be running as well Andrea Leadsom, Minister of State for Energy.
Ann Widdecombe, Christian and former Conservative MP, told Premier's News Hour who she is backing.
She said: "I am emphatically supporting Andrea Leadsom, you must have someone who supported Brexit during the campaign, otherwise that persons commitment to getting Britain out won't be taken seriously in Europe and it won't really reassure the majority in the country who voted to leave."
Ms Widdecombe told Premier Ms Leadson is competent and calm: "During the entire campaign she never lost her rag once, and the very next day after the campaign when all the financial markets were going mad and the media was hysterical - she's got a big background in finance - and she was asked what about the markets and she replied very calmly 'they will recover,' and they have."
Gary Streeter, Christian and Conservative MP South West Devon, told Premier's News Hour he is impressed with the line-up of believers.
He said: "There are probably more Christians at Westminster now than ever before, two of the candidates are very strong Christians, it's great that all candidates are acknowledging the importance of faith in the public sphere.
"God is not dead, he's very firmly alive and on the throne."
He said he will be backing Stephen Crabb.
David Cameron stepped down as PM on Friday after the UK voted to leave the European Union via referendum vote.
Next, Conservative party MPs vote until there are just two candidates left, then the wider party membership take a postal ballot to elect a PM.
Listen to Premier's Marcus Jones speak to Gary Streeter here:
Listen to Premier's Marcus Jones speak to Ann Widdecome here:
