PrestaShop to Shopify Plus — Zero-Downtime Migration

A UK lifestyle accessories brand was running on PrestaShop 1.7 — a platform fast approaching PHP 7.2 end-of-support, held together by 23 third-party modules of varying quality and a hosting arrangement that pre-dated the iPhone. The store was processing £85,000/month and the founder had watched two previous migration attempts fail: one abandoned after 6 weeks when the agency ran out of scope, one completed but rolled back after checkout broke under real traffic. The business had been burned twice and the trust deficit was total. When they came to us, the first conversation wasn't about Shopify — it was about how we'd approach the risk differently. With £85K/month flowing through the store and Christmas trading 14 weeks away, a third failed migration would likely end the business. We proposed a parallel-run migration with a hard go/no-go gate at week 8: if Shopify wasn't fully validated under synthetic load by that point, we'd delay rather than go live into uncertainty.

• Mobile checkout abandonment of 68% — 4.2-second load times on mobile were haemorrhaging conversion, and the PrestaShop theme was built in 2015 before mobile-first was even a consideration
• PCI compliance failures — their payment provider had flagged the checkout flow as at-risk and given a 90-day remediation notice, which was 6 weeks away
• Zero ability to run promotions without developer intervention — every flash sale required a code push and a maintenance window, making reactive trading impossible
• SEO rankings declining month-on-month as Core Web Vitals failures compounded — the site had slipped out of the top 10 for three previously-owned category keywords
• Two previous migration attempts had failed — the business had a well-founded fear that this would be a third

We executed a phased, zero-downtime migration from PrestaShop to Shopify Plus — preserving every product, customer record, order, and SEO ranking through a disciplined parallel-run cutover. The work was sequenced around risk: solve the PCI compliance issue first, then the conversion problem, then the migration itself.

• Complete audit and normalisation of 2,400+ SKUs — 12 years of inconsistent product data cleaned, deduplicated, and restructured before a single product moved
• Custom Shopify Plus theme built mobile-first from a blank canvas, engineered specifically for LCP <2.5s across all product and category pages
• Custom Node.js ETL scripts for all data migration — no off-the-shelf migration tools, because every one of them has edge cases that silently corrupt historical order data
• 1:1 URL redirect mapping for 14,000+ product and category pages using Screaming Frog crawl analysis, preserving all existing SEO equity without a single 404
• Two-week parallel run with hourly automated inventory sync keeping both platforms live; Saturday 2AM cutover slot chosen for minimum traffic, achieved in 22 minutes flat