1538 archdeacon of Warsaw. A few months later he declined King Sigismund's offer of the bishopric of Cujavia, and in the autumn probably of the same year (1538) he left Poland for Frankfort, lodging there in the same house as Hardenberg, and the two travelled together to Mayence, whence Laski left for the Netherlands.
In 1540 Laski settled at Emden in East Frisia. In 1542 he became pastor of a congregation in the town, with a general charge as superintendent over the surrounding district, and an official residence in the Franciscan friary. In this office Laski appeared as a reformer of the Swiss school. His views were extreme, especially in regard to the Sacrament, and he cleared his churches of what he held to be idols. Yet he was no favourer of the anabaptists, and had difficulties with Menno. The form of church government which he established was presbyterian, for which the Frisians were prepared by earlier customs of their own. In 1544 it was decided that four laymen from the congregation should assist the minister in the regulation of discipline. To Laski was due the cœtus, or assembly of ministers, which gathered at Emden once a week from Easter to Michaelmas, and examined into the life and doctrine of its members. For his congregation he prepared in 1546 his 'Catechismus Emdanus major.' This was used for some years, and superseded by the 'Heidelberg Catechism,' which was partly based upon it. In the spring of 1546 he ceased to be a superintendent, but remained a pastor. In 1547 he formed a friendship with Hooper (Hooper, Later Writings, Parker Soc. ix.), through whom, and through the foreign protestants who had settled in London, Laski became well known to protestant divines in England.
When in 1548 Cranmer began to scheme for a general reunion of the various protestant sects, he invited Laski to come to England to attend a public conference on this subject (cf. Cranmer, Works, Parker Soc., pp. 420–1). Laski arrived at the end of August 1548, and spent the winter at Lambeth. An order of council of 23 Feb. 1548–9 gave him 50l. (Acts of Privy Council, 1547–50, p. 244), and he left England for Emden in March 1549 (cf. Works, ii. 621). On the 22nd Latimer in a sermon said: 'Johannes Alasco was here, a great learned man, and as they say, a nobleman in his country, and is gone his way again: if it be for lack of entertainment, the more pity' (Works, i. 141; cf. Zurich Letters, iii. 61, 187; Cranmer, Works, p. 425). He returned to this country 13 May 1550, lived for some time at Lambeth (ib. p. 483), and on 24 July 1550 was appointed superintendent of the London church of foreign protestants, who included many of his Frisian congregation, and to whom the church of the Augustinian Friars was assigned by letters patent 24 July 1550 (cf. Luckock, Studies in the History of the Prayer Book, p. 67). In 1550 Laski took Hooper's side in the controversy as to vestments (Hooper, Later Writings, p. xiv; cf. Zurich Letters, iii. 95), and Hooper's attitude may be largely attributed to Laski's influence. He organised his church on the presbyterian model, and must be regarded as the founder of the presbyterian form of church government in this country. He still actively supported the extreme reformers in their long controversy with the Lutherans respecting the sacraments. In September 1550 Laski visited Bucer at Cambridge, and had a long discussion on religious matters. They differed on the question of the Real Presence. Bucer wrote down his opinion, and Laski prepared comments on Bucer's views, which were published in his 'Brevis et dilucida de Sacramentis Ecclesiæ Christi Tractatio,' London, 1552. On 6 Oct. 1551 Laski was appointed one of the divines on the commission for the revision of the ecclesiastical laws (Zurich Letters, iii. 678). The result of the commission's labours appeared later as the 'Reformatio Legum;' on 19 Nov. 1551 he received a present of one hundred French crowns (Acts of Privy Council, 1550–1552, p. 420). His influence at the court of Edward VI was great, and can be traced in the second prayer-book and in Cranmer's later views (cf. Gasquet and Bishop, Edward VI and the Book of Common Prayer, pp. 173, 230, 232; Cardwell, The Two Books of Common Prayer Compared, Pref.), but the production of his own liturgy seems to indicate that this influence was not as successful as he wished (cf. British Magazine, xv. 612, xvi. 127).
On 15 Sept. 1553 Laski embarked at Gravesend with 175 of his congregation (Zurich Letters, iii. 512) on his way to Poland. A storm drove the ship to Elsinore, and though the king of Denmark received Laski favourably, other influences prevailed, and they were driven away in midwinter. They had no better reception at Hamburg, Lübeck, and Rostock, but the main body found shelter at Danzig, while Laski managed to reach Emden and remained there for more than a year, chiefly through the intercession of the Countess Anna of Oldenburg. On 31 Dec. 1555 Laski was reported to be dangerously ill at Frankfort, where he remained during the first half of 1556. He employed himself in superintending the churches, holding a disputation with Velsius, and trying to