Her family moved closer to Geelong, and she attended Sacred Heart College, where she was a member of the debating team and elected deputy school captain in her second year.

At university, Credlin resided at Newman College, won a number of prizes and awards, and was a member and national finalist of the 1995 Philip C. Jessup International Law Moot Court Competition Team.

After graduation, she was admitted as a barrister and solicitor in Victoria, and applied for a job as a political staffer with Liberal senator Kay Patterson in 1999.

[5][better source needed] She obtained a Graduate Diploma in Legal Practice with distinction from the Australian National University (ANU) in 2010, where she won the ACT Law Society Prize for the top student of 2009.

[citation needed] After working for several years on Patterson's staff, Credlin moved to become an adviser to Senator Richard Alston, the Minister for Communications in the Howard government.

Tired of the commute between Melbourne and Canberra, where her husband Brian Loughnane was based, Credlin returned to her career as a political staffer, working for senators Robert Hill and Helen Coonan.

[20] In November 2021, she joined anti-vaccine mandate protests in Melbourne, where members of the crowd carried prop gallows and chanted anti-Andrews slogans.

[26] In June 2021, Credlin was appointed an Officer of the Order of Australia in the 2021 Queen's Birthday Honours for "distinguished service to parliament and politics, to policy development, and to the executive function of government".