Mr Clark said his daughter called him every night no matter where she was in the world, and if she could not get through she always texted him.
He described his daughter's career achievements as "awe-inspiring".
"I have nothing but admiration for Helen's achievements.
"It was very much her decision to put her hand up for the top UN job, and as her greatest supporter I'm 100 per cent behind her decision.
"Helen was always a very independent little lady and she knows her own mind."
If Helen Clark needed any endorsement, in her father's words, she could tell the United Security Council that she came to the role "from a little country with no baggage".
Mr Clark said there was always a special spark in his oldest daughter's eyes.
"From the moment I clapped eyes on her lying in a cot in the hospital ward, and saw her piercing blue eyes staring back at me I knew we were in for an interesting ride, as it has proved to be."
Her race for the position of the United Nations Secretary-General also has the backing of the New Zealand Government.
Yesterday, Prime Minister John Key announced the Government was nominating Helen Clark for the position.
"Having served as the prime minister of New Zealand for nine years and held one of the top jobs in the United Nations for the past seven, Helen Clark has the right mix of skills and experience for the job," Mr Key said.
"There are major global challenges facing the world today and the United Nations needs a proven leader who can be pragmatic and effective.
"Coming from New Zealand, Helen Clark is well placed to bridge divisions and get results. She is the best person for the job."
Mr Key submitted New Zealand's nomination letter to the Presidents of the UN General Assembly and the UN Security Council.
"Helen Clark has a vast amount of experience in international affairs which will be hard for other candidates to match. She's a great listener and communicator, and I know she will make a difference if elected."
She became the Administrator of the United Nations Development Programme on April 17, 2009 - the first woman to lead the organisation - after serving three terms as New Zealand's prime minister.
She has entered a race that so far has seven other competitors.
Helen Clark said she was honoured to be nominated.
"I'm running because I believe my style of leadership is needed and will help the United Nations face the serious challenges ahead," she said.
The new Secretary-General will be appointed at the end of the year by the UN General Assembly on the recommendation of the UN Security Council.
additional reporting NZME
