The place of his birth was Reval (present-day Tallinn), Estonia, which at the time was a Swedish dominion where Magnus Gabriel's father Jacob De la Gardie served as governor.

Jacob De la Gardie, Count of Läckö, was a prominent military commander who served as Lord High Constable of Sweden from 1620 until his death in 1652.

[2][3] Father of Jacob, and grandfather of Magnus Gabriel, was Baron Pontus De la Gardie, a French mercenary who had been in Danish service but made a career in Sweden after having been captured by Swedish troops in 1565.

[7] These seven were Magnus Gabriel, Maria Sofia, Jacob Casimir, Pontus Frederick, Christina Catharina, Axel Julius and Ebba Margaretha.

His skill and interest in these areas was in demand during a time when individuals in power should not only be well-learned, resolute and rooted in history, but have a sense of details and possess splendour as well.

[2] In 1646, De la Gardie was head of a diplomatic mission to France in order to find Queen Christina musicians for her Swedish court.

[11] On 17 April 1648, he was promoted to general and served as such under the future king, and his own brother-in-law, Charles Gustav, during the Siege of Prague that took place in the final months of the Thirty Years' War.

[2] In 1652, he became Lord High Treasurer (riksskattmästare), which was one of five Great Officers of the Realm and, as such, one of the most prominent and powerful members of the Privy Council as well as head of the Kammarkollegiet.

He and his family had to leave the court and for the rest of Christina's reign, De la Gardie lived on his manors in some kind of an exile.

However, Queen Christina abdicated soon thereafter and was replaced on the throne by Charles Gustav, the brother of De la Gardie's wife Maria Eufrosyne.

It appears that De la Gardie was anything but a splendid military commander, as he received much more complaints than praise from the king for his actions in that area.

In accordance to his will, De la Gardie was appointed Lord High Chancellor and, as such, member of the regency that ruled Sweden during the minority of Charles XI (1660–1672).

This may have been due to the fact that he was, reportedly, unable to work enough, and that he often left the court to spend significant time on his different estates, a disadvantage for both the government and De la Gardie's own position of power.

[2] Being experienced and having many important relationships, he was a prominent member of a regency but he looked too much to the past and the traditions during the Thirty Years' War and therefore lacked a vision suitable to the demands of a new era.

De la Gardie was the main representative of the party in favour of warlike adventures and a close relationship to France.

[2][11] The opinions of De la Gardie's side most often won out and, therefore, Sweden was nearly drawn into wars against Russia and Poland during the regency period.

[11][16] In a Sweden with great financial problems, these subsidies was, in Count De la Gardie's thinking, a more attractive way to improve the state's finances than a reduction, which would mean that lands granted the nobility would be reclaimed by the Crown.

[2] De la Gardie himself was responsible for parts of the financial troubles Sweden faced at the time, created by Johan Palmstruch and his paper money.

[2] The harsh conditions in the latter half of the 1670s, with the war as the main cause, could be attributed to the treaty with France, for which De la Gardie had been a spokesman.

[13] In 1675 a special commission was appointed to inquire into the doings of De la Gardie and his high aristocratic colleagues, and on 27 May 1682 it decided that the regents and the senate were solely responsible for dilapidations of the realm, the compensation due by them to the crown being assessed at 4,000,000 riksdaler.

[2] De la Gardie had been partly responsible for the treaty with France and had worked hard to increase the young King Charles's power.

It might seem ironic that the treaty helped moving Sweden into a deep crisis financially, which, together with the level of power Charles had attained, in turn led to the reduction.

[2] On 7 March 1647, in the chapel at the Royal Palace Tre Kronor, De la Gardie married Maria Eufrosyne of Zweibrücken.

Moreover, De la Gardie owned large properties in Livonia, Finland, Pomerania and Mecklenburg, at the time all parts of Sweden.

In 1674, the Italian diplomat Lorenzo Magalotti estimated that De la Gardie had at least 50 on-going projects in Sweden and its provinces, excluding the 37 churches he was constructing or repairing at the time.

Architects, sculptors and painters were brought to Sweden, to make contributions to De la Gardie's constructions and restorations.

[30] De la Gardie's ancestral home provides a chilling backdrop for the short story "Count Magnus" by Montague Rhodes James.