The phrase to take one’s courage in both hands means to muster up all one’s courage.

It is probably a calque of the French phrase prendre son courage à deux mains. The earliest occurrences of this French phrase that I have found are from the following two books:

1-: From Mémoires du Duc de Rovigo, pour servir à l’histoire de l’Empereur Napoléon (Paris: A. Bossange, Mame et Delaunay-Vallée, 1828), by Anne-Jean-Marie-René Savary (1774-1833), 1^st Duke of Rovigo;
2-: From Le Cocher de fiacre, ou quarante ans sur le pavé de Paris, roman de mœurs (Paris: Lecointe et Durey, Corbet, Pigoreau, Tenon, 1828), by Auguste Ricard (1799-1841).

The phrase to take one’s courage à deux mains has occasionally occurred in English; for example, in The Wedding Ring: A Tale of To-Day (New York: Cassell Publishing Company, [1891]), by the British poet, novelist and playwright Robert Williams Buchanan (1841-1901)—“à deux mains” is in italics in the original text:

“You seem agitated, Mr. Bream. No bad news, I hope, of your parishioners?”
“Oh, none! Things are going splendidly.” He stopped short, and then, taking his courage à deux mains, plunged at the communication he had to make.
“I have learned a thing this afternoon, which closely concerns you,” he said. “It concerns you so closely, it is of such vital importance, that I scarcely know how to approach it. I am afraid that it will be something of a shock to you.”

The earliest occurrences of the phrase to take one’s courage in both hands that I have found are as follows, in chronological order:

1-: From Napoleon and the Ploughman, published in The Albion (Liverpool, Lancashire, England) of Monday 23^rd August 1830—this unsigned text was probably reprinted from some book or magazine:

“This mention of the kind feeling entertained by the first consul towards the humblest soldiers in the ranks reminds me of the following occurrence which took place at Malmaison. Early one morning Buonaparte strolled from the chateau in the direction of Marly. He was dressed, as usual, in a gray riding-coat, and accompanied by General Duroc. As they walked and chatted together, they observed a labouring man guiding his plough as he approached them. ‘Hark you, good man,’ said the first consul, suddenly stopping, ‘your plough is not straight; you seem to be ignorant of your trade.’ ‘It would puzzle you to teach me,’ said the countryman, eyeing the well-dressed strangers from head to foot. ‘Not in the least.’ ‘Aye, aye, well, try,’ replied Hodge, giving his place to the first consul, who, seizing the handle of the plough, and driving on the horses, commenced his lesson. So awkward, however, was the experimental agriculturist, that the furrow soon swerved most unconscionably from a right line. ‘Come, come,’ said the peasant, roughly seizing the first consul by the arm, and resuming his place, ‘your work is not worth a button: every man to his trade; stick to yours.’ Buonaparte continued his walk, having first remunerated the peasant for his moral lesson by putting two or three louis into his hand, as a compensation for the loss of his time. The labourer, astonished at the amount of the donation, hastily quitted his plough, and related his adventure to a farmer’s wife whom he met on his road. The latter, having obtained a description of the stranger’s costume, guessed that the generous donor was the first consul, and communicated her discovery to her simple companion. The honest rustic was at first stupified [sic] with amazement; but the next morning, arming himself with resolution, and attired in his best, he made his appearance at Malmaison, and demanded to speak with Napoleon, to thank him, as he said, for his handsome present. On my acquainting the first consul with the arrival of his visitor, he ordered him immediately to be introduced to his presence. While I went forward to announce him, the peasant, to use his own expression, had taken his courage in both hands, to prepare himself for the important interview.”

2-: From Singular Biography, published in The Birmingham Journal (Birmingham, Warwickshire, England) of Saturday 24^th November 1838—this unsigned text was probably reprinted from some book or magazine:

“Gian Batista, the little collector, was admitted to sing, with a troop of abominably bad performers, at the Theatre di Romana. The evening before the representation, the prima donna had suddenly disappeared, leaving her companions in the utmost consternation. Seduced by the cigar-smoking, phrase-making graces of a French travelling clerk of a mercantile house, she had accompanied his return to France, and, in a few days afterwards, he repaid her in kind the trick she had played her lyrical brethren, by setting off for Paris one morning without her, before she had left her couch. But in the meantime the unfortunate company were in the utmost distress. What was to be done? All the world was expected to assist at the representation, and the prima donna was wanting. The father of Gian Batista came to their relief. He passed the whole night in teaching his son the part of the prima donna; and Gian, taking his courage in both hands, soon mastered all the difficulties, and the next night, dressed as a woman, sung the part, was rapturously greeted, and, for the first time in his life, heard the sound of that applause with which, later on, he was destined to become more familiar.”

3-: From Chapter III of The Twins of the Hotel Corneille, published in The Nation (Dublin, County Dublin, Ireland) of Saturday 29^th November 1856:

Leonce and Dorothea wrote to each other every day in verse and prose, and it was amusing to see them exchange billets, under the shelter of a handkerchief on [misprint for ‘or’] the shadow of a fan. The Baroness was gratified to witness these little stratagems; she had loosed the bridle on her daughter’s heart; she permitted her to love M. de Baÿ.
Towards the end of February, Leonce took his courage in both hands: he made his proposal. M. and Madame de Stock, informed of it by Dorothea, received him in solemn audience.

The Twins of the Hotel Corneille is a translation of Les Jumeaux de l’Hôtel Corneille, published in Les Mariages de Paris (Paris: L. Hachette et Cie, 1856), by the French novelist Edmond About (1828-1885)—the original text is as follows:

Léonce et Dorothée s’écrivaient tous les jours, en vers et en prose, et c’était plaisir de les voir échanger leurs billets, à l’abri d’un mouchoir ou à l’ombre d’un éventail. La baronne s’amusait de ces petits manèges : elle avait lâché la bride au cœur de sa fille ; elle lui permettait d’aimer M. de Baÿ.
Dans les derniers jours de février, Léonce prit son courage à deux mains : il fit sa demande. M. et Mme de Stock, avertis par Dorothée, le reçurent en audience solennelle.