[1] Mary Elizabeth Donaldson was born 5 February 1972 at Queen Alexandra Hospital in Battery Point, a suburb of Hobart, Tasmania.

[2] She is youngest of four children to Scottish parents, Henrietta (née Horne), an executive assistant to the vice-chancellor of the University of Tasmania, and John Dalgleish Donaldson, an academic, mathematics professor and member of the Clan Donald.

She became a trainee in marketing and communications with the Melbourne office of DDB Needham, taking a position of account executive.

[10] In June 2000, Mary moved to a smaller Australian agency, Love Branding, working for a short time as its first account director.

In the (Australian) spring of 2000, she became sales director and a member of the management team of Belle Property, a real estate firm.

[10] Mary met Crown Prince Frederik of Denmark at the Slip Inn[15] in 2000 during the Summer Olympics in Sydney.

On 24 September 2003, the Danish court announced that Queen Margrethe II intended to give her consent to the marriage at the State Council meeting scheduled for 8 October 2003.

[34] Following the wedding, the Crown Prince couple embarked upon a summer working-tour of mainland Denmark aboard the royal yacht Dannebrog, then travelled to Greenland and the 2004 Athens Olympics.

[35] In 2005, during the celebrations for the 200th anniversary of Hans Christian Andersen, the royal family was involved in related events throughout the year.

[38] During a Council of State on 2 October 2019, the Queen's request to appoint Mary a rigsforstander, a functioning regent when the monarch or the heir is out of the country, was approved by the government.

After having sworn to respect the Danish constitution, she became the first person not born into the royal family to assume the position of rigsforstander since Queen Ingrid in 1972.

[39] Mary was voted Woman of the Year 2008 by the Danish magazine Alt for damerne, donating her cash reward to charity.

[54] In the context of immigrant issues in Denmark, Mary has visited the disadvantaged migrant areas of Vollsmose (2006),[55] Gellerup (2007),[56] and Viborg (2010),[57] and has participated in integration projects including the teaching of the Danish language to refugees.

[58][42][59] As patron of the Danish Refugee Council, Mary visited Uganda (2008)[60] and East Africa (2011)[61] and supports fundraising for the region.

[62][63][64] Mary has played an active role in promoting an anti-bullying program based on an Australian model through the auspices of Denmark's Save the Children.

[70] The foundation's aim is to improve lives compromised by environment, heredity, illness, or other circumstances that can isolate or exclude people socially.

The initial funds of DKK 1.1 million were collected in Denmark and Greenland and donated to Frederik and Mary as a wedding gift in 2004.

[71] In 2016, on the International Day Against Homophobia and Transphobia, Mary gave a speech on LGBT rights at a forum in Copenhagen hosted by the Danish government.

She called for an end to discrimination, oppression, and violence against people on the basis of sexual orientation and gender identity.

[76] She carried out numerous engagements in connection with the event and also gave the closing speech of the week-long celebrations on 21 August 2021.

[82] Several of these, including a gala dinner at Rosenborg Castle, were cancelled due to the ongoing COVID-19 pandemic, but several hundred Danes showed up at Amalienborg's courtyard at noon on Mary's birthday.

Rather than stepping out onto Frederik VIII's Palace's balcony as is customary for birthday celebrations in the Danish royal family, Mary and her three oldest children came out onto the courtyard to thank the people who had shown up.

The main field of Mary's coat of arms is Or-coloured and shows a MacDonald Gules eagle and a Sable-coloured boat both symbolising her Scottish ancestry.